They're frightened of poverty and government control, which they have been brainwashed to associate with sane and progressive policies.

If the economic future of your town relies on the coal, oil, or gas industry, then anything that threatens to disrupt that industry is a threat to your future. Sure we could invest in public projects to educate and rehabilitate those losing their jobs to technological progress, but that would mean the big bad gubmint getting involved, and you've been taught by everyone you trust since childhood that the government doing anything is tantamount to the devil. The only option left is to fight tooth and nail against any and all progress.

These people are not insane, they're acting perfectly logically in accordance to a flawed understanding of reality, an understanding which is in part manufactured by the ruling class to prevent the growth of leftist ideas. They're not stupid, they're ignorant, scared, desperate, misled, and yes, sometimes very bigotted. There's a reason cults recruit outside hospitals, and the cult of 45 is no different.

They're frightened of everything the other commenter mentioned, but they forgot something: they're frightened that, if "their team" loses power, they will get treated the way they've been treating "the other team" for ages. The grifters know they're lying when they spew their shit, but their followers believe it because it's what they've already done, just in reverse.

"Liberals want to destroy Christianity" is believable because xians have tried their damnedest for nearly 2 thousand years to destroy other religions. "The transgenders want to force all children to change gender" is believable because they've spent decades forcing children into their view of gender, and killing, torturing, or raping them if they don't conform. "Gays want to outlaw heterosexual marriage" is believable because they outlawed gay marriage for ages. "Minorities want to force white people into labor camps" is believable because slavery.

They believe that everyone thinks exactly like them, and they can't fathom that some people want everyone to be happy. They think we're lying when we say that, putting on a front to lull them into a false sense of security just so we can pull the rug out from under them. Because it's what they would do, given the opportunity. And they're terrified of it being turned around on them.

Edit for clarity - and those other things, the vaccines, the healthcare, etc etc, may seem unrelated, but it all comes down to making sure "the other team" doesn't get any "wins". Because if "the other team" wins, that's one step closer to their team losing, and one step closer to "the other team" being able to enact all those horrible policies against them instead of in their favor.