I can think of exactly one guy: a classmate in electrical engineering courses who was from Kentucky. While you can obviously still find accents in the US, there are lots of reasons why you won't run into that family of accents much. Just about everyone in the US can avoid accents they don’t want by engaging in all forms of audible media, and social climbers and people who move around will avoid strong accents. Those are the same people who will filter to the top of any affirmative action cohort and end up at elite schools.

Maybe the redneck culture of poor Appalachian people is less sticky than the redneck culture of many poor Blacks in the US. My personal anecdotes support that, but then selection bias means they necessarily must.

When I run into guys at work with heavy Appalachian accents, they tend to be heavy machinery mechanics. That's also where I find Black guys who cling to a large amount of Black redneck culture. And those two groups together comprise the supermajority of heavy machinery mechanics at work, come to think of it.

Source: I spent my entire childhood on counties adjacent to what is considered 'Appalachia', and I went to a higher-end college with a significant affirmative action focus on geographic distribution around the US.