Well, part of current instruction is the dogma that “illegal immigrant” is a “race,” so you’ve got to think the fascinating variety of both pre-contact and contemporary Latin America is of no interest at all.
And you can partly blame popular culture for some of it. They are too lazy to crack a book so when they need a tribe they make them either Aztec or Maya.
They have had them as far north as North Dakota and as far south as Peru.