I happen to know a bit about game and simulators. From a plane's point of view, houses dont look unique. A small number of models is enough to fairly represent most houses. There may be a minority of structures that are really unique (stadiums, bridges, landmarks, ...) but the vast majority of buildings aren't unique. Even if two building have different heights, it's possible to reuse textures if they're built from the same material.

MSFT appears to have designed the simulator by considering every building is unique, but if they compared buildings and textures, ideally using automation, they would see there's a massive amount of duplication.