I wrote about more or less this topic a while ago, you can read it here but I will provide a brief summary.

Partially there is a simple aspect of time depth to it, the cultures of the Chalcolithic Danube ("Old Europe") have really only been known in a significant way since the post war period. Compare that to, say, Egypt and Mesopotamia, which not only had a spot in the European consciousness due to the Bible and Ancient Greece, but also had major, headline grabbing archaeological expeditions in the nineteenth and early twentieth centuries.^1 The other major reason, and more relevant to the question of more well researched works that should be less subject to whims of popular imagination, is that it is difficult to easily place Old Europe in a "Story of Civilization" in a way that is not true of something like Catalhoyuk. It was a period of spectacular early urbanism, but it also did not really lead to a successor culture, this is not to say it was a "cultural dead end" but the urbanism of the Iron Age Mediterranean looked to the east, not the north. It is an awkward fit for those who have set ideas about how civilizations rise and fall.

This relates to your direct question, which is why it is not considered a "civilization" the easy answer is: it is, increasingly. But these sites have been subject to an enormous amount of scholarly debate about what to call them, are they "cities" "proto-urban areas" "mega sites" or some other ad hoc scholarly formulation? That is because they lack many of the features that we have on the checklist of early urbanization: visible material hierarchies, monumentality, centralization, physical definition, etc etc. If you think of cities as not just a bunch of people living together but also a social formation with particular social features then these sites don't really match what we expect to see from early cities in the way that, say, Ur does. So what do you do? Do you say that these are cities even though they seem to be part of a totally different social process than all the other things you call cities? Or do you say they are "mega sites" even though they are more populous than the thing you call "cities" in a different context?

Anecdotally I would say the reluctance to call them "cities" has been falling away for all sorts of reasons in scholarly trends and fashions, and they are increasingly discussed as early urban sites. But this is going to take a long time to percolate to the popular consciousness.

^1 The Indus Valley Civilization is somewhat more comparable in that regard but there are two important factors to that case: one is the hugely important role it plays in the national self image of several very large, culturally important, populous and heavily Anglophone countries, and secondly the personal celebrity of Mortimer Wheeler, the charismatic celebrity archaeologist who was its most important early excavator

More can be always said >!(drink!)!< but similar questions are asked on this sub quite frequently, for example https://reddit.com/r/AskHistorians/comments/w4mtle/how_is_mesopotamia_concidered_the_cradle_of/

TL;DR: difference between a "culture" and a "civilization" is to a degree arbitrary, but the most widely used definitions include "writing" in the list of prerequisites, thus in absence of some new world-shattering archeological discoveries no culture before the Sumerians can be considered a civilization.

Perhaps this may also be a question for r/AskAnthropology.

I discussed this in another thread recently.

I think the top comment here has you covered though.