Thanks you, that makes a lot of sense.

So the very brief version is that there was just as much cultural diversity in eastern Mesoamerica as in the west; it's just that more recent events have led to the umbrella label "Maya" being applied to a disparate collection of cultures in the east, whereas no similar umbrella label has been applied to the west. (I suppose because "Aztec" already exists as a lazy label for anybody who doesn't want to get into the actual diversity in the region.)