That is a complex issue, and the reality is that pronunciations develop regionally. It happens in the UK as well as in North America. There is probably only one correct formal way to pronounce a word, but many different ways it is actually pronounced.
One word that really irritates me is the the word “important”. I believe I pronounce it the correct way, but many others including Millennials pronounce it in a slang form that I find irritating. They turn the first “t” into a “d” (to my ears). And the one well known guy that I notice it the most with is Jagmeet Singh (our NDP leader). What I hear him say is “impordant”, and it just grates on my ears… However if you look for the correct pronunciation on line, you will find some people go to great lengths to say that the “correct way” is actually the “wrong way”. And I think that is the basic root of the problem. If we don’t like the right way, just do it the wrong way, and declare it the norm. I suspect that is where all the regional dialects start from. We copy each other, and decide it is right. In any case here is a link which goes over the ways to say “important”.
If you really want an experience just go to a remote rural part of Newfoundland like Fogo Island, and try to understand a conversations between two long time locals. They will change their language to talk to a “townie”, but between themselves it is simply not understandable. It seems to be some combination of Scottish, Irish, English, Gaelic, and perhaps a Viking or two thrown in!