So once upon a time, America was a place where anyone could come to get a good job. In fact, if you were walking down the street in the middle of the day, someone would stop you and say, "Come work here, please." Practically begging you to get benefits, a pension, and you could buy a house on your salary.

This is because manufacturing was a huge part of the post-WW2 booming American economy, they needed bodies to run the machines, and you didn't have to know anything or be specially trained, you could just go in and start being productive on day one. Shows like Mad Men, where a bunch of men were sitting around, getting paid to think, that was far more rare than it is today. Most people did something in a factory or warehouse.

Then, international trade became increasingly cheaper. Then countries with poor human rights (ie slaves) were able to undercut companies who were using an American workforce to produce the same product. As execs cut costs to keep up, the workforce became more opinionated, some forming unions, which increased the cost of labor. So beginning in the 60's and 70's, they started moving all the manufacturing overseas to areas with cheaper labor. My parents were from Baltimore, they and their parents and everyone they knew had all worked at Bethlehem Steel at Sparrow's Point (a mill producing steel) almost their entire lives. In the 70's they started decreasing the workforce, then it got sold to a German company, who moved most of the operations overseas, and by the 90's my grandparents were basically forced into retirement with a great pension and health insurance, as guaranteed by their union.

Oddly enough this is exactly what happened with the great recession in 2008: overseas companies started offering less-regulated investment opportunities, this put pressure on our own oversight to deregulate - which they did. Then American businesses started packaging more and more risky home loans (called sub-prime loans), and investors were buying them at prime rates because home loans were such a sure thing.

I remember from my life, in a suburb of DC, when a poor family moved into the neighborhood. They had habits that we were not familiar with, to put it politely, and they kinda stuck out like a sore thumb. They only lasted a few months, then got foreclosed on. Basically what had happened was there was pressure on banks for more home loans, so they started offering loans to people who couldn't normally afford a house, and probably didn't fully understand the implications of a home loan. The bank probably just told them "Free Money!" and they said ok. But then they couldn't pay, and this happened so often everyone probably remembers something like this happening around that time.

So anyway, globalization has caused these small towns that used to house workers for a factory to become frozen. Usually around the time the mill closes or massive layoffs happen, workers will move to greener pastures, businesses that relied on them will close, leaving the town in whatever state it's in. And that's why you see so many towns exactly like what OP is describing.