It's not sudden. At all. The coal industry has been on the decline for quite a while now, and green jobs have been on the rise.
As if blue collar workers are not professionals.
I find it hard to see a machinist not as a professional but fine, I'll change my internal dictionary.
Reading https://en.wikipedia.org/wiki/Professional it looks as if this is a cultural difference.
Edit: thinking about this a bit longer, it seems clear that the distinction was made by those who don't get their hands dirty at the expense of those who do, and it seems extremely demeaning to me. As if the 'white/blue collar worker' distinction wasn't bad enough now people who spend a lifetime acquiring the knowledge to do their jobs are not even allowed to be called - or call themselves - professionals.
That doesn't seem clear to me at all.
"Moreover, people invest a lot in building up a professional identity, which helps make the work more bearable (and, by giving people pride in what they do, probably ensures that the work is better done). Suddenly abandoning something that has constituted a major part of who you are, and taking a job at the bottom of a new field, is not any easier for a machinist or a coal miner than it would be for a professional."
https://www.bloomberg.com/view/articles/2017-01-06/some-blue...