Should have asked them how did English colonists way back in the 1700’s wind up loosing that English accent? Well, okay, there is Boston. But how did American accents change over the years? Aussies retained a semblance of the English accent and they’re about as old as we are considering immigration.
If you watch movies from the 1920s and 30s, you can still hear the English accent. It must be the influence of immigrants from so many other countries who all learned to speak English.
I just read that the southern drawl is from the Scotch Irish combined with french and spanish.
The answer is actually simple. OUR today’s ENGLISH is derived from people who spoke English, German, French, Italian, Yiddish, Polish, Chinese, Spanish and most of the other languages of the world. The children of those immigrants, got put into schools, learned English and also saw that that IRISH girl in the next row was kind of cute, and she thought the ITALIAN guy was pretty neat.
The getting together of those children is the thing that is today called the American “Melting Pot.” Words from all the European countries became a normal part of OUR language.