High there, I’m a mechanical engineer with a study of material development through history.

The problem of iron production and quality in iron grade depended largely on what time period and where in the world the production was taking place. In OP’s original link they y’all about the early years of iron production right after the initial spread of its knowledge in the Middle East and eastern Mediterranean (where the hittites conquested through). In these early days (just like the early days of any material) very little is know about what the material characteristics are like. Especially in the days before modern approaches to metallurgy which are based off the atomic lattice structuring and how certain alloying elements interject themselves within the principle elements structure. In the early time period for metal production of any kind (Bronze Age forward) smiths relied solely on trial and error and missteps within normal metal production and the recognition of the smiths in the change in quality of the metal and its performance characteristics. Early bronze and brass alloys came about from different copper ore deposits that happened to also contain the ore for the alloying components too (brass - copper & zinc, bronze - copper & tin). This types of deposits are not common and the recognition of newer deposits of the individual elements and their exploitation would be key factors in the trade between early empires (copper from the Anatolian region would be traded to metal producers in Crete who would also import the tin from an entirely separate region. All this effort exerted in the goal to make bronze metal for tooling and weapons).

Back to the area of iron production: empires that started to produce iron metal would run into the same quality control problems as their ancestors of the Bronze Age. With the caveat that the mixing (or alloying) of two or more different metals can yield different characteristics (strength, resistance to deformation, flexibility) on the resulting combination was more common knowledge now from all the experience learned by the copper and bronze ages (in addition to other metal working techniques, cold working, annealing, etc).

However iron ore behaves very differently from those of copper, tin, zinc, gold, silver, lead, or any other metal that was available at the time of irons introduction on the world stage. Firstly being that the main element that has an affinity for bonding and alloying with iron is not another metal but is carbon. This causes a big issue because of the way metal is created from raw ore. Ore is typically oxygen bonded with the metal (copper, iron, tin, zinc) on an atomic scale (though it does occur with plenty of other elements, these ores are not what are used historically to create metal). The way these ores are turned into metal is by breaking the bonds and removing the oxygen so that the metal remains by itself. Traditionally this was done is a furnace, which although a common word today does not share any aspects apart from the general use of heat. Ancient ore furnaces while differing in appearance were all equally constructed of ceramic (bricks and mortar, or a single ceramic piece) and were fed by charcoal produced from wood. Materials that are easily available locally in most regions of the world. The charcoal would provide the fuel to heat the raw ore (with the air or forced air to increase the heat output and temperature) and create carbon-monoxide (CO). What the ancients didn’t know was that scientifically the reaction was at the elevated temperature the CO would react with the ore metal oxide and would strip away the oxygen atom(s) form the metal atom(s). The heated metal atoms (in the case of iron) would combine into larger groups and form droplets that would be suspended in a spongy matrix of metal drops, unconverted ore, unburnt charcoal, and impurities. This iron “bloom” as they are called would then be worked with hammers to remove the charcoal, remaining ore, and impurities and consolidate the small metal drops into a larger metal ingot that could be used to create tools and weapons.

Remember about irons affinity for bonding carbon? Well charcoal is a source of pure carbon and when the iron ore is being converted to metallic iron it has plenty of time and opportunity to bond with carbon and the resulting amount of carbon in the alloy can be high, low, or any ware in between. Carbon can be removed from iron by heating to high temperatures where the carbon is literally burned off from the iron carbon alloy, but in a historical method of heating with charcoal this is a fuel and time expensive endeavor. However to work iron in any usable fashion the smith needs to heat it. So in the process of producing a sword or weapon the uncontrolled heating of the iron to form it causes an uncontrolled amount of carbon loss.

This is part of what causes issues with iron quality and replicating good iron batches. The chaotic ore converting process and the subsequent working process to create useable tools and weapons will easily leave an uncontrolled amount of carbon in the iron. In modern study only iron with an alloyed amount of carbon from 0.8%- 3% by weight (some schools can differ those amounts by ~0.5% but this is the general range) results in what we would classify as steel. With better strength (and other) characteristics steel was highly sought after in all tool and weapons production. Anything higher than 3% and it results in very brittle cast iron (not a normal product by this method) anything lower and you get close to pure iron which is very ductile and soft (not as soft as bronze mind you but still softer than steel).

This can and was worked around by the smiths being skilled enough to identify and select specific batches of iron from production that are closer in the steel range and using those for only the highest grade of weapons, by being skilled enough to work the ore conversion process to result in more steel grade metal, or by a variety of other methods. Either way the result is that when smiths DID have the knowledge to create or identify good steel from low grade iron it took more time, effort, and resources to do so. Expensive things have always been highly prized throughout history and early steel items were of no exception.

This brings use to the second issue plagued by smiths which was alloying impurities in the iron. Not all combinations of element with iron results in a better end result. If alloyed with too much sulfur this can cause embrittlement even if the carbon % is in the steel range. So WHERE the iron ore came from is just as important as HOW they converted the ore to useable metal.

As an example (which isn’t of the early Iron Age but gives insight to the same issues they would face) smiths in the Middle East during the Middle Ages recognized that batches of iron made from ingots with ore originating from the western Indian subcontinent happened to perform better than ingots obtained from other suppliers in our local region. This was the foundation to the “legendary Damascus steel sword on the medieval period in the Middle East. The reason for this better steel was because of a low sulfur and other impurities content in the ore used in its production. With less impurities the steel can out perform other weapons of lesser quality and garner a reputation of almost mystical properties.

But being able to source good ore is an issue ever since the Bronze Age. War, famine, and other factors can disrupt trade and cut off resources from other regions as it did in the case of Damascus steel.

So to summarize: the prize possession of steel products in history was due to the difficulty of producing said steel. By means of lack of knowledge, it’s time, energy, and resource intense production methods, and the ore available to use in those production methods.