Zoom way out to the national level. Looks like the empty towns in the middle of nowhere do the best -- because they force you to move out to get a job. Also, no one there is having decent jobs just appear locally in front of them, so you have to make yourself look good on paper to get one of those far-away jobs.

There are other factors that obviously affect this, but looks like that's the real dominant factor. Drastically changing location is the best way to quickly increase wage, and these towns do that, like tossing a young bird out of a nest.