There are two points to make about your question.

The first point is that the idea itself of governance being something that needs to spring from an autochtonous source is a relatively modern one. For centuries, governance was in the hands of aristocratic families who either fought each other for territory or married each other to acquire it or keep it in the family, regardless of the ethnic or language groups of the people who lived on the territories.

Looking at the family tree of any monarch, even the ones who ruled France, you will immediately be struck by the fact that their families are anything but local.

For example, Louis XVIII of France's mother was Maria Josepha of Saxony, his maternal grandfather was Augustus III of Poland. His paternal grandmother was also Polish: Maria Leszczynska. Going back one step further, he had a great grandfather who was Joseph I, Holy Roman Emperor, who married Wilhelmina of Brunswick, the other relatives of that generation are from Bavaria, Sardegna, Denmark, Brandenburg, Wurttemberg, etc. They are not "French".

The second point is that what you perceive to be "some form of national identity" is something that you are observing after the political unifications have taken place, i.e. after generations of schooling and common media have had their effect on the language people speak in the public arena. It is really not so evident that Italians had a national identity before the unification. The statesman Massimo d'Azeglio wrote after the unification that "We have made Italy, now we must make Italians", to illustrate the point.

If they were separate countries today, say, as a Duchy of Parma, a Republic of Venice, a Republic of Genova/Liguria, a Kingdom of Piemonte, a Kingdom of Sardegna, a papal state of Rome and a Kingdom of Naples & Sicily you would probably see this as a status quo that is just as natural as any other: as has often been commented on AskHistorians, even today it is difficult for north Italians and Sicilians to understand each other: the mafia trials in the 80s and 90s used interpreters.

In fact, those are very much the lines along which Napoleon (who was very aware of national identity) divided the peninsula: he created the Kingdom of Italy whose geography only extended to North East Italy, a separate Republic of Liguria, and a separate Kingdom of Naples.

The short answer: the earlier European "nations" were creations of political machinations, which created with conquest, marriage, and tradition the rough boundaries of what would later become something like "French" or "English". Germany and Italy were never dominated decisively by a central government like the so-called "nation-states", however, and therefore did not unite until dramatic changes in political situation, and the emergence of so-called "national consciousness" (at least among elites) made their existence both conceivable and attainable.

The somewhat longer answer:

First, I want to reiterate that the other European countries did not "unite" in the way that Germany and France did. When France came mostly under the rule of a single king (at the end of the Hundred Year's War, regional variations within "France"—let's say, from Gascony to Normandy, or from Provence to Brittany—would be more pronounced than the differences on the borders between France and other countries. People within a single "nation" could not understand one another, and culturally they would share little or nothing in common. No one in any part of France would consider themselves "French" in a way that signified a cultural, social, or national identity that reached across the territory; rather, France was wherever the local nobility owed their fealty to the King of France. There is, frankly, no inherent reason that "France", the nation we know today, should exist. If it had been split in any number of a dozen ways before the 18th century, that configuration could easily look just as natural to our eyes.

As for why Germany and Italy didn't follow this same progression, we need to look at the Holy Roman Empire, the decentralized political unit which covered Northern Italy, Germany, and, until 1648, the Low Countries and Switzerland. Ruled by a nominal "Emperor", who was chosen by the seven Electors after the Golden Bull of 1356, the Holy Roman Empire was really a very loose collection of feudal territories, cities, merchant republics and prince-bishoprics. Unlike elsewhere, the balance of power never shifted decisively in favor of a single dynasty, and the individual princes within the Empire were able to rule their territories with only slight interference from the Emperor.

Northern Italy was kept splintered by the individual wealth and tradition of its various city-states and small feudal states, and by near constant foreign interference. City-states would routinely switch between allegiances, bouncing between supporting France, the Holy Roman Emperor, the Pope, and each other in struggles. These fluctuations in power would continue until the Napoleonic Wars, when Napoleon conquered the entire peninsula. Southern Italy, for its part, was consistently much poorer than the North, and was firmly dominated by Aragon and then the united Spain up until the 19th century (when, again, Napoleon conquered it), preventing any union of North and South, should the North have ever been united.

Germany, it should be said, is a very large and populated country, with more than one major axis of trade in the medieval and early modern periods, and tremendous cultural diversity. If someone in the 17th century was to use the word "Germany", they would mean what we now call Germany, as well as a number of now-separate territories: Switzerland, Austria, Alsace-Lorraine, and the modern-day Netherlands. This is a truly vast stretch of land, and no single entity could ever control this territory.

The basic outlines of German "disunity" are fairly similar to Italy's, but expanded: individual states are too powerful to reliably control each other, and are willing and able to unite politically to maintain their individual rule. At various points, several hundred entities within the Holy Roman Empire, most of them German, gave fealty to the Emperor alone; since the Emperor was very weak compared to most other kings in Europe, they were all effectively independent. Compounding this problem was the lack of reliable primogeniture in most German dynasties: each son would receive a share of the land, resulting in ever-growing numbers of smaller territories. A prince (most famously the Margrave of Hesse) could have wonderful successes diplomatically or militarily, and come to dominate regionally, only to break it apart into a dozen pieces within two generations. The only princedoms which were legally indivisible were the four secular Electorships: Saxony, Bohemia, the Palatinate, and Brandenburg, and they were all dominant within their own sphere. By the 18th century, Brandenburg-Prussia dominated in the north, while Austria, whose Hapsburg dynasty were the Holy Roman Emperor for the entire early modern period and were Kings of Bohemia, dominated the south; even at this point, however, neither had full control over their "half" This system would last until the 19th century, when as you might predict from the Italian example, Napoleon invaded and formally dissolved the Holy Roman Empire.

Further Reading:

Thomas A. Brady, German Histories in the Age of Reformations, 1400-1650

Brennan Pursell, The Winter King: Frederick V of the Palatinate and the Coming of the Thirty Years' War

Mark Konnert, Early Modern Europe: The Age of Religious War, 1559-1715