This is actually an interesting point Den and I have read it myself, although I can't remember where...hmm. Perhaps it was in this book "The Story of English" or perhaps I read it elsewhere but I did read it. I live in New England and it is true that the English there is the more pure to the form it was originally, before it mutated over in England over the years. But then the U.S. also started getting the immigration influx as well after the days of the Puritans and Pilgrams we had Italians, Irish, Germans etc. so after that I am sure the language mutated AGAIN but interestingly it is these mutations that allowed English to become the dominant language over French. When the Saxons and Viking and Romans conquered England, it was the ability and ease that English adapted words and made new words from other languages that gave it a 'one up'. When organism and languages are able to evolve and adapt they become stronger, live longer and become dominant. The English language is fascinating in it's ability to do this and not become something else. The fact it remained over all of the languages of 'invaders' is truly astounding and I highly recommend the book below
https://www.amazon.com/Story-English-Third-Revised/dp/0142002313