You know these things are a little nebulous and hard to pin down, and I'm not going to pretend to be able to verbalize it perfectly since I'm doing it as an outsider (I'm not a red state voter. I live in NYC). But I can tell you what I've seen. (cont . . . )
I have family in the Midwest and I've seen some of these towns. I think it may be related to the unions that were destroyed (30 or 40 years ago). And then how it emptied things out and killed the soul of those communities; a sense of vibrancy and knowing and caring for neighbors.
On top of that they can see they have no meaningful or sympathetic (or even just non-hostile) representation in the sense-making institutions of our culture (journalists, universities, and artists). So they turned to toxic waste like talk radio and fox news.