I think you are overestimating the ease of people moving from one place to another. While job may be a primary reason people live in the cities, there are other important reasons like access to entertainment, shops, being close to other friends who leave nearby etc. It's not as simple as saying "oh, I could spare 500$ a month by moving in the middle of nowhere, let's do it". Not everybody wants to live in suburban/rural areas and spend most of his time at home.