That is a really interesting question. It is also one, I have to confess in advance, on which we do not have any hard data. At least this is so to my knowledge and it will remain so unless there is a sort of a sociologist of historiography directly asking scholars why they did so. In the meantime, as a researcher of the field, I can share with you my own view. In my view, there are three factors at play here. As an initial note, I should say that there are, of course, many books not called Atatürk on history of the Turkish War of Independence, the work of Erik-Jan Zürcher or Feroz Ahmad being some examples that spring to mind. That said, you are correct since 'Atatürk' titles are very common in this field, often enough uncommon elsewhere.

The first one is that, as you note as well, Atatürk was the pivotal figure in the history of the Turkish War of Independence, in addition to being a charismatic person. Charisma is a bit of a difficult tool to handle in historiography, for obvious reasons. It is like that other thing that was once defined as 'I know it when I see it'. Most people, contemporaries and modern people alike, agree that Atatürk was a very charismatic person, who always dressed up in an excellent fashion, whose manner of speech was a certain way, and so on. Combine this with the fact that Atatürk really was alone in some moves he initiated. Take the alphabet reform in 1927, for example, towards which the clear majority was either suspicious (that is, not opposed to it as a principle but fearful for how quickly it was to be implemented) or simply opposed. Something similar seems to have happened with the proclamation of the Republic. So, this paragraph's main idea is that this focus on Atatürk is not fully an invention based on nothing. A fact that is almost never explicated but often tacitly assumed in social sciences and history is that the impact individuals have on the course of history is not equal. Atatürk was one of those who were very impactful and who also had the charisma to boost this further.

That said, it is clear that a single individual, Atatürk or anyone else, ever brings about a social phenomenon by himself/herself, let alone winning a war or changing the course of a whole nation. It is always a combination of individuals, with their different beliefs and desires pulling history towards various directions. Therefore, the first factor is very important but does not by itself to explain this focus on Atatürk.

This is where the second factor comes in, which is that Atatürk the man was something and Atatürk the symbol was something else, albeit related to the former for obvious reasons. For haters, Atatürk is where all those demonic ideas such as Westernising and secularising Turkey. For those who love him, for the reasons mentioned above, he is the one who made it all ultimately. As a central figure, he thereby becomes the central figure of polarisation and debate as well, since both his opponents and supporters agree that he was the one that made the difference. I suppose the polarisation is key here as well; the more those who love him see those who hate him, the more Kemalist they become, and vice versa. Thus, Atatürk becomes the central point of debate.

Though this looks very political, it is not simply politics. This is because, first, as before, to some degree, the pivotal role attributed to Atatürk is actually accurate, and second, because historians do not exist in a bubble. They too are influenced by the politics around them. If nothing, there are always some historians who are quite political, which then motivates other historians to tackle their problematic views. As most politically-minded people take Atatürk as the centre of criticism/praise, history becomes like this too. A related dynamic is the very existence of debates on the role of Atatürk. You have someone like Sukru Hanioglu for instance, always very critical of the way Atatürk is perceived as 'THE' figure of modern Turkish history. Naturally, people like Hanioglu cannot just ignore a mountain of scholarship and attitudes which (for criticism or praise) take Atatürk as the central figure, and therefore he too starts talking about Atatürk. He even wrote a book called Atatürk... Though, I have to say, this debate does get confusing at times. Seemingly, everyone agrees that no history can be written based on one heroic individual, and yet the debate somehow goes on.

Add to this the fact that non-Turkish academics or intellectuals are not isolated from all this process either. They too may have sides, they too may be drawn into the same methodological or political debates whether they have a side or not, and so on. They are subject to all that is said above as well. You can also see that non-Turkish specialists can be particularly sensitive to the reigning political atmosphere in the country. Kemalism or Atatürk as historical phenomena never change as they happened, in that the alphabet reform will never be undone in 1928 (unless Elon Musk does something he will really regret). But our view of them changes with time, both as people with an interest in politics and as historians. This is natural, as the philosopher of history Arthur Danto has wrote long ago on how a historical action may attain different meanings depending on subsequent events, even after its actors are long gone. More thoughts on Atatürk lead to more debates on his role, which, in turn, lead to more books.

Finally, the third factor. Considering all these, ask yourself this: which book would sell more? One called 'Karabekir' and the other 'Atatürk' with appropriate subtitles. To begin with, most non-Turks would not even know Karabekir. Then they would question why you would name a non-biographical book on Turkish history that way when there is a more pivotal figure around. They would also be surprised that whatever your viewpoint is, you are simply (at least apparently) sidestepping decades of debate on Atatürk. Therefore, fewer sales for you.

Sales may even be the wrong word here. Not all of us care that much about selling our work but we do, presumably, care about being read. Why else not think of it but write and publish? Again, the more sensational name is Atatürk because non-Turks know it too, because there is a debate and therefore a passionate reader profile, as well as the fact that you are not simply creating sensation and can get away with such a title. I mean, though a single individual alone does not move the country, writing a book on modern Turkish history called Atatürk is not like writing a history of music from its very beginning to our day and calling it '50 Cent: The Making of Music'.

I hope this was helpful!