Why do people dislike new european civs despite the majority of civs already being non-european & the game itself is eurasia-centric?

The answer is simple [and it doesn't have to involve political correctness or idle complaining]:

1. Generic tech trees: all civs in aoe2 are built on a common tech tree, but european civs have the MOST generic tech tree (i.e., no camels, no parthian tactics, no battle eles, no eagles, no steppe lancers, & no Unique units based on eles or camels). Conversely, there is nothing in the standard tech tree that euro civs have access to that non-euro civs don't. People like gameplay flavor, and european civs start at an inherent disadvantage compared almost all other the civs in the game because of their exceptionally bland tech trees. This also limits the novelty of euro civ bonuses and unique techs, since, for example, you can't have a battle elephant oriented unique tech if you don't have battle eles...
2. Architecture! A large part of the attraction of new civs is the immersion into a new culture and a new area of the world that has its own unique stories. A large part of that immersion is appearance of the units, buildings, etc. of the civ. No new architecture set = no new eye candy to draw in interest. One or two new UU skins or wonders is less satisfying.
3. Novel geography / climate / culture matters. Again, immersion into a new region of the world is a large part of the allure of new civs and the enjoyment of new campaigns. The novelty is important, and I think realistically more people would be more excited to play civs and campaigns about unexplored areas of the world, than re-tread stories about the 100 years war [and Joan of Arc] from a different perspective. And I'm not that people can't or shouldn't be excited about that too, just it is unsurprising if they are much less excited.

This is NOT to say that the new European civs are bad, it is only to say that it is very understandable why are a large number of people seem to be miffed by the latest civs being what they are. And, whether those people are right or wrong, more expansions seem likely in the coming years that will hopefully explore other areas of the world!

^\Note: There is room for debate about what civs are historically more "necessary" / what civ's absence in the game is most strongly felt, but this gets too controversial and arguments about it are generally pointless])