There's only 50,000 people working in coal mines, and if you x10 for related businesses, that's only 500k people out of a country of 330M. I can't imagine this constitutes a "good portion" of this country (USA).
Also, those mines are heavily subsidized, basically $80K per year in subsidies / tax breaks per miner. Effectively they're being paid a government wage to keep mining.
What you're seeing here is a large section of the population that likes the idea of coal mining, and willing to spend a lot of tax money to keep that idea alive.
A large section of those states’ populations maybe. On a national level, they’re only relevant because of their ability to swing votes from one party to the other.
Working in coal mines, and working to support coal mines, aren't entirely the same thing. (More than) Half the country is against government provided healthcare, but that doesn't mean half the country works in private medicine or is immune to disease and injury.
Access to healthcare affects every single person and their community in a pretty obvious way. I don’t see any reason to assume people other than those in the coal industry and maybe their family and friends to care much about it. Maybe a few more for political ideology, but I still can’t see it being a significant amount.
The only reason we hear so much about it is because the states with coal industry hold some swing Senate and Electoral College votes.
I am not in the US. But your point is actually in support of my last sentence :). Of course, I do agree that there are a bunch of worse work environments.
https://www.eia.gov/coal/annual/