People didn't choose to live there, they have always lived there. Most people in rural US didn't pack up and move in the last few years but have been people that have been there for generations. Now it's easy to think they can just pack up and moving, but packing up and moving to an urban area is very expensive in the actual cost and with no guarantee that there's something that might be as stable as what you have in your rural area. Some of these people in those areas are the farmers that grow the foods that we eat btw, and they can't do their massive large scale farming in the city.