I think that 'accents' develop because of the lack of movement of populations. Until WWII, most Americans never traveled farther than five miles from their birth place. When people wanted to hear Elizabethan English spoken, they went to Appalachia in the U.S., because that population was isolated from its start. This isolation compounded the accents or drawls. As mobility has increased, the accents have tended to disappear or become a part of the whole. The Kali4kneeyaisms: 'Like' and 'you know', have become a part of the whole. With education, the Brooklynese 'toity toid' for '33rd', and 'erl' for oil have mostly disappeared. (This, of course, does not apply to the present occupant of the White House. The heavier his phony drawl, the more he is lying.)
Yet, here in America, the Brooklyn accent is universally understood; whereas someone from crowsfeets, texass, can't be understood. Pantagathus will most certainly attest to this.