I mean, back when ToAU came out we barely knew anything about the Near East either, but I think people really liked ToAU because of cool aesthetic and they took advantage of their mostly blank slate to create new lore and such. As early as RoZ (arguably in Vanilla) everything we were told about the Far East meant they would have to go with a very specific aesthetic, and CoP just solidified that more. I guess maybe they just didn't want to do Japanese-y theme?
The decision for Wings was probably cost-saving measures. I mean, even ignoring the mostly recycled areas, half the story there was already written for them really.
After that we had years where we thought Wings was going to be the last Expansion, and along comes Adoulin, which was a place we knew almost nothing about. But this time the team was probably even smaller than it was during Wings, so I wouldn't be surprised if their lack of resources is part of why they chose somewhere we knew little about so they could do the whole colonization theme as a excuse for those relatively closed areas with all the hallways and such. Adoulin's lore/culture also doesn't feel as well planned-out as ToAU's did.