I’ve never been to Charleston. (With a Walmart right up the street, I hardly even go to Charlotte ;-).
Teachers from up north, maybe? I’ve read that’s why natives of New Orleans talk like New Yorkers.
I have been speaking Texan for the last 50 years. Problem is it keeps coming out like south Brooklyn.
I’ve noticed a lot of people from the coastal areas of the southerns states (Savannah, GA excluded) don’t have much of a Southern accent. And all other the South accents tend to be much thicker in rural areas that in the big cities. I guess that’s to be expected. The Yankee influx in the big towns are the reason for that. I have not lived in NC for 45 years, but never lost my accent and never wanted to. If you’ve ever heard Richard Petty talk you know what I sound like.