there's just a lot of land that is far away from cities that is a bit inhospitable in one way or another especially in the centre of USA, it's similar in australia, mostly desert or low scrub, not much water, really hot summers.

people live in trailers and hovels out in the boonies, work at mines or logging or farming, wherever there is especially a lot of farm land. i've seen sparse areas of eastern europe, and they are not much different, usually there is a gypsy neighbourhood especially in bulgaria, off the side of most small towns, and they are pretty poor.