From a humorous perspective, how should US pronounce "wash" from a Wisconsin accent (sounds like "warsh"). Or how to pronounce "car" or "bar" from a Boston accent. (sounds like "cah" and "bah") Southern's in the US say "ant/aint" instead of "aunt". And what about "y'all"? etc, etc...
Maybe there is similarities with the varied UK accents?
In fact, English dialects in the British isles have huge variety compared to those in North America, by at least an order of magnitude. It sounds counterintuitive at first because the differences in land mass and population size are the other way around, but the actual biggest factor here is the amount of time that these regions have had English-speaking communities. Give it a few more centuries and the rate of local dialect differentiation will start to catch up.
American English dialects trace back to the various British groups that settled the different colonies. Tangier Island[1] for example has an ancient Cornish dialect. Ocracoke Island[2] has what is probably the closest thing to a living Elizabethan English speech community. Those are extreme examples, but the stereotypical New England and Southeastern dialects have similar origins, they're just considerably watered down due to the lack of isolation.
Meanwhile, the standard "BBC English" Received Pronunciation is actually quite the novelty, comparatively speaking.
Maybe there is similarities with the varied UK accents?