It was somewhat surprising to me just how few coal mining jobs exist. Learning that there were fewer than 50,000 left in the nation really got me puzzled why it was made such a hot topic in the election. It's clear an industry that is one it's way out and has been for a long time, but I guess people not wanting to deal with reality has been a theme of Trump's success.
Some groups of people have an outsize influence on politics, and also in the cultural mindset. Coal miners are those people for Appalachia, as even at the peak of coal employment it wasn't *that* huge (only 250k nationwide, as an article upthread said).
It just got mythologized as the ideal job of the postwar boom, similar to the mythic heavy industry jobs, a place where a man could go after high school (or maybe after the Army) and make a living to support a wife and three kids and a nice house in the country.