Armor making was considered a highly valuable craft for that time and armorsmiths that could forge plate mail were held in high esteem. Initially, armor production wasn't controlled by guilds and depended a lot on local government influence and organization. The earliest armorers in the Milan area ran their craft in small shops or family businesses, working on a small scale operations and partnerships. The "booming" popularity of plate allowed those families to become rich and potentially led to the expansion of the craft to other parts of Europe.

Later, Guilds throughout Northern Europe held a tighter control throughout its production. No longer any family could start a small shop and produce plates. To become a certified and licensed master armorer, one had to indenture for four years as a journeyman and be examined/licensed for each component of the armor. Sometimes they even had to submit yearly "samples" to be examined. So it took many years of training and experience to legally produce a full harness. The fact that shops were restricted to 1 master, 2/4 journeymans and 1 apprentice meant that the quantity of produced armor was very limited. There were some exceptions to this kind of tight control, notably on the Milan area, which had more relaxed guild control and thus made the area a source of "workforce" and armor production in the period.

The Milanese armorers were renowned and sought after. In fact, the first armorer known by name was Aramano Rubei, recruited in 1232 to start a mail making operation in the city of Vercello. In the 15th C., 24 Milanese armorers were recruited to France, 11 going to the area of Lyon.7 This cross regional dispersion of armorers was a factor in almost all the major production centers from Augsburg and Innsbruck to Greenwich.6 The movement of these craftsmen would have helped the process of dissemination of technique and practice and the true secret of the master armorer would have been in the details and experience of the individual, especially in the heat treating process.

Armorsmiths that could produce quality plate were treated almost as a "tactical asset" to local governments. Their specific techniques and details were held as a trade secret. In a time where dozens of different governments were scattered through Europe and local power struggles were common, a contingent of 30 renowned armorsmiths could be a very valuable asset.

Thus, combining all those factors like scarcity of certified master armorers, difficulty to establish a legal shop outside guild control and government influence, the craft itself (refined techniques and details of the production process), availability of raw materials and difficult/long training one had to endure to be able to master the craft, plate production wasn't disseminated across Asia and other regions with the same ease, particularly due to cultural and geographic differences (it would be more preferable for a capable armorer to practice his craft in Europe rather than move all the way to Eastern regions).

Ps: Sorry for all the grammar mistakes and typos. English isn't my first language.

Source: http://www.oakeshott.org/metal.html

As I have mentioned in my replies to other comments, this is a very difficult question. It requires us to definitively say what factors led to Plate Armour’s development in Western and Central Europe, and to explain in what way those factors were absent in other places. In many ways, we should reverse the question - why did Europeans develop plate armour? European style plate armour is not the historical norm, after all. Why was Europe different? Why didn’t late medieval Europeans stick to mail, fabric, lamellar and scale armours like the most of the rest of the world for most of history?

There is no definitive answer for this, yet. There are many factors, and as a starting point we can list them out. But we cannot, say which factor was completely decisive. To do so we would need to know everything there is to know about warfare in both Medieval Europe and everywhere else.

There are a number of factors that are conditions for the development of plate armour. We know that they contributed in various ways, and a number of them are absolutely necessary for its development. I will divide these into ‘supply side factors’ - those which made plate armour possible - and ‘demand side factors’ - those which made plate armour -desirable-.

On the Supply side, making plate armour requires the following:

• A relative abundance of iron ore and the ability to mine it. This is rather obvious. You need to get the metal out if the ground in order to make it into armour.

• The ability to create relatively high-quality blooms of iron or steel in excess of 10 kg or so - the size needed to make a breastplate from a single bloom. In order to make a large, strong, single plate of metal, you need to start off with a large and high quality piece of metal, produced all at once. Welding together multiple pieces of metal produces lines of brittleness along the weld, which will produce weaknesses in the final metal plate. So you need a bloomery big enough and hot enough to produce a very large bloom of decent iron or (better) steel. For much of European history, blooms weren’t big enough. And that plate armour that existed was made of smaller pieces - either rivetted together (like a great helm, which was assembled from multiple pieces) or held together by some kind of backing (like a coat of plates.); the largest piece of metal used as armour in the 12th century would be the skull of a helmet. By the 14th century, though, average bloom size increases towards 10 kg, making larger plates and thus more solid pieces of armour possible. There are a number of factors that lead to this, but waterwheel-powered bellows certainly helped.

• The ability to turn that bloom into a sheet. This is a good deal easier, but making a large bloom into a sheet of metal requires a lot of work. Watermill powered hammers, introduced in the later middle ages, makes this process much easier. This makes plate armour more economical.

• More generally, the economic organization to assemble all the pieces from ore to bloom to plate into a finished product. None of the above happens in a vacuum and a society needs a relatively urbanized and specialized economy to turn steel into plate armour, compared with mail or fabric armour.

Demand Side Conditions

• Someone to pay for plate armour. You need a social class or organization or government that can pay the tab for this armour. A warrior elite might fit the bill, so might a king paying for small semi professional armies of contractual soldiers.

• A way of war that makes fighting in plate armour practical. Not all methods of fighting are conducive to the use of heavy armour.

• The presence of high energy weapons. These are weapons that can penetrate other forms of armour. They include:

• Crossbows

• Lances, wielded couched in a mounted charge

• Polearms

• Early Firearms

These conditions were all present in later Medieval Europe and played a role in the development of plate armour. This is not necessarily an exhaustive list, and as such it is hard to proceed from here to a definitive explanation for why plate armour did not develop elsewhere.

Followup question: Didn't the Japanese Samurai use a form of iron plate? I know there was lots of cloth and leather involved in the construction, but isn't it still considered plate?

Can the Historians here provide a context regarding the year spans we are talking about here?

What is the earliest known use of plate armor and the like? When was it at its zenith of use?

First of all the logistical aspects of the use of plate armor are necessary to consider. Full plate armor was something that was reserved only for those who could afford it, certainly the fantastic plate armor you talk about is of the most expensive and limited variety, and furthermore certain levels of training were necessary in order to maneuver in the battlefield. As such it's understandable that soldiers in plate armor were limited in their numbers in comparison to soldiers with inferior equipment, they were the nobility, the elite of society. A professional military force of highly armored men wasn't something that could easily be adopted, developed and maintained. This explains why would lower quality armor be preferred, there has to be a balance between cost and effectiveness, and indeed plate armor was pretty expensive and not easy to produce in large quantities. In this light the European armor wasn't the rule, it was the exception, so along with answering why it didn't spread outside of it, it's also important to understand why it developed in the first place. As such, the adoption of a tactical system that revolves around heavy infantry/cavalry like that which developed in the middle ages in Europe depends on how effective it is in the military context of a society, while taking into account it's cost and the resistance of preexisting military tenets to adapt.

In regards to Europe a rather particular way of warfare developed during the middle ages, which could very well be traced back to the Greek and roman ways of warfare, and it was that of decisively defeating the enemy with a frontal charge. The Greeks were certainly very fond of such tactic with their phalanx formation, designed to face the enemy head on with an energetic charge, and while the Romans throughout their various conflicts adopted more flexible formations and lighter troops for skirmishing, the strength of their army remained their heavy infantry. In the middle ages this trend continued in Europe in the form of the knights, who came to create a warrior culture revolving around their chivalric code and became the center of the European battlefield with their shock cavalry charges. For this warrior class which had the monopoly on a particular military skill, the strengthening and imposition of said way of conducting war becomes an important part of it's culture. And in this context in which being a knight and bravely charging at the enemy is the greatest achievement of any man, and the main objective of the infantry is to face said charge, the technological developments that occurred during the middle ages seem pretty reasonable, both the development of heavy plate armor and pike formations and mass use of projectile weapons to counter it. As costly as it was, heavy shock cavalry tactics fit perfectly with the European conception of war and it's development further shaped it to be that way. While this doesn't necessarily explain the why, as it is a very difficult question which depends on many factors, it at least explains the context that allowed it to happen, but how does this context differ from that outside of Europe?

Elsewhere heavy cavalry did exist and was used effectively time and time again, but it didn't have such a great importance like that of the European knight, this is because unlike in Europe frontal charges weren't the norm, it tended more towards skirmishing, hit and run tactics employing fast, lightly armored troops, something that in contrast was something that Europeans lacked. There is a reason why crossbows, and later firearms, were used by most of Europe instead of bows, because it required less training to use, and as such was preferable as a ranged weapon since Europe mostly lacked an archery tradition, because that contradicted the face-to-face nature of it's conflicts, with of course the notable exception of the English with their longbowmen. These soldiers were heavily disliked by the nobility, since they could cowardly and very easily defeat an armored knight safely from afar with hardly any training, it was seen like as if breaking the rules.

In the open plains and steppes that can so commonly be found across Asia, along with the generally harsher climate, another military skill better suited for this terrain had developed: Horse archery, and it was heavily influential on the military tactics of this part of the world. Indeed the Ottomans, as you talk about them, along with the seljuks and ayyubids who faced the crusaders, among many other groups, had a very strong horse archery tradition. The armies of the east were fast and flexible, and relied on harassing, skimishing, flanking, avoiding direct contact with the enemy, only charging selectively at weakened sections of the enemy formations, and feigning retreat to draw the enemy into an ambush. This is drastically different from the European style, and in this context plate armor was not necessary to invent nor to adapt, as it was slow and cumbersome, instead the horse archer took the main role in the battlefield, an unit which, as well as the European knight, was very hard to equip and train, and as such it represented the elite of the army, meaning that such a drastic change in their tactics and equipment was not seen as something that ought to be done, regardless of benefits or advantages over the old ways, similar to the European issue with the crossbows. This is important to understand, because nowadays war and technology are almost synonymous, but the pursue of military technological developments was dictated by the needs and beliefs of society more often than a necessity to find the objectively best technology like in modern times. This not only means that war was more a cultural, traditional aspect of society, but also that there was hardly ever any "cutting edge technology" able to stomp anything else in the battlefield, as sometimes people tend to think of longbows, firearms and plate armor, instead tactics were often more important.

And the thing is that both tactical systems brought something different to the table, both with advantages and downsides, and the crusades are probably the most representative of this, with the constant interaction between both systems. On one hand there's the battle of Hattin, in 1187, in which Saladin of the ayyubids lured the crusaders out of their defensible encampment at the La Saphorie springs by conquering the fortress of Tiberias. As the crusader army left the encampment they suffered constant harassment by the Muslim skirmishers, and eventually cut off their line of retreat, leaving them surrounded under the arid sun that affected the heavily armored knights and without water. The next day demoralized and thirsty the crusaders still charged desperately at the Saracens only to fail time and time again as the waves of arrows wore them down until defeat was absolute. Then there's the battle of Arsuf in 1191, in which, after the Muslims' ineffective harassment and failure to cut the crusader supply lines, they decided to ambush them at a forest, however, the crusaders managed to keep the cohesion of their ranks in the face of constant attack by the muslism and eventually led a counter attack that resulted in the muslim rout.

While the tactics were varied, which one to choose is not something that depends only on the tactics themselves, wars don't happen in a vacuum, there are plenty of factors, and as such tactics need to suit and adapt to their terrain, their climate, their culture and customs, their political and economic situations etc. So while the european plate armor might have been really effective, it doesn't negate the usefulness of cheaper, lighter armor in a different tactical system

I do know that it did in one instance spread beyond Europe as it was used among the Japanese (after 1543, however plate did exist in the 5th century in Japan in the form of iron helmets and cuirasses). Not only were European cuirasses imported, but Japanese began constructing plate armors of their own while incorporating more traditional armors. These Japanese-constructed armors frequently imitated European armors or took on forms of their own.

Imported plate armor would be prohibitively expensive, but some Daimyo ensured that their entire army was equipped with plate-type armor.