It's a bad cycle. Imagine you're the "wealthy" person in a town of poor, jobless people. What local businesses do you spend you time and money in? Groceries and gas? Both are probably not locally owned, so most of what you spend leaves the area. You drive 2 hours on weekends to get to the nearest Walmart to buy clothes, so again most of your money leaves the area: and none of the places you're spending at employee lots of people and/or pay them lots of money. Most of the jobs servicing those industries will be part-time anyways.

For the people who work in the mines, they make more money, but they honestly don't really know what to do with it...and there's nothing in particular to spend it on locally anyway.

Even worse, arable land is a rarity, it is a mountain area! So it's hard to even build a local agricultural economy. It's isolated from transport links, landlocked and hard to navigate. If you pick a route from anywhere East of Appalachia, and take it to San Francisco or L.A., you'll be routed entirely around the area in favor of a Northern or Southern route.

I didn't grow up in Appalachia, but I grew up in an area not too different from it. Honestly, if we hadn't been within commuting distance of a major city, my career options would have been farm work or gas station attendant. There wasn't even enough of a commercial sector for "retail clerk" to make the list.

It's a useful thing to drive through that area: it's stunningly beautiful, but you start to get a feel for why there's so little going on there.