Suburban America is an incredibly CLEAN place to live. Especially because many people drive a LOT and walk very little. So, for many Americans, depending upon where you live, it can be seen as ‘village’ behavior – meaning that you’re used to being dirty. Or City behavior (meaning the same). And it can be pretentious (or insulting) to ask guests to remove their shoes. Within the past few decades its become fashionable to keep house shoes inside, and separate shoes outside.