There are not many people living in those smaller blue-collar cities.

I grew up in an exurb of a larger city, and most of those I grew up with live close enough to where they grew up that they meet in back in the home city every weekend to be with friends and family. The larger point is most people already live in a metropolitan area and remain in that area. It might be a different city within it, but still the same area.

I'll guess in your case while most kids did leave the town you grew up in, most moved just a few hours away to a city. As opposed to many hours away to a city in a different state.