Is it the same sort of situation that Africa is in where the conditions are too harsh to get much done? Was is simply a cultural thing or what?
Edit: I don’t mean this in a racist sense I’m just genuinely curious as to why.
This is a very broad question that can't really be answered in one post, but you should look at the wiki page for Pre-Columbian American history. You might also want to look at the section on Africa's level of development.