To be fair, a European emphasis been the case with all AOE games.
AOE1: A majority of civs are either European or directly related to the rise of Western civilization (Palmyra, Assyria, Sumeria, etc.). Only four of seventeen civs are outside of that classification, with Choson, Lac Viet, Shang, and Yamato. No sub-saharan, indian, or amerindian civs are included at all.
AOE2: 22 of the 43 civs, more than 50% are European, with some euro civs split with incredible granularity (for example: goths, Burgundians, and Franks are all related to France), whereas the entirety of China is represented by one.
AOM: 3 of 5 civs are European. Greek, Norse, Atlantean (basically knock-off Greece). Egypt and China are the odd pantheons out.
AOEO: 4 of 7 civs are European, and the other 3, Egypt, Babylon, and Assyria are closely related to Western civilization.
AOE4: 5 of 10 civs are European, with no amerindian civs and only one African civ.
Heck, when AOE3 launched, all 8 civs were European, and up until DE, 8 of 14 civs were European. So the current 11 of 22 euro civs with 2 quasi-European civs (USA and Mexico) is par for the course.
The focus on updating Euro civs makes sense given this background knowledge. They’re the oldest in-game civs, largely untouched, and account for 50% of civs. Thus, updates will often feel like a Euro update.
There are lots of compounding reasons for this trend, and none of that is worth debating here, as it is all outside the realm of playing a game. From a game developer’s perspective, they are simply updating the oldest civs to be more in line with newer civs.