America is diverse in some ways, but in terms of language and dialects (which is what we're discussing here), America is remarkably homogeneous. There are many tiny countries with more linguistic diversity than the US.
Specifically to english and dialects, you are correct. England proper has a different dialect and accent for every nook! London for literal neighborhoods! It also has several hundred if not thousand of years on the US for language to develop. Africa has everyone beat on this front. Bantu alone has who knows how many sublanguages! America has done a pretty remarkable thing in keeping its language internally consistent despite it’s overwhelming cultural diversity and influences! That it sucks to learn for the uninitiated is exactly for this reason.
