Another key factor is that a lot of baby boomers are reaching retirement age. With every kid being told college is the only path to become "successful," there's going to be a lack of talent in the trades at least in the near term that's going to continue driving wages higher.
I've been teaching college students at non-elite schools for ten years, and it's obvious to me (and pretty much any intellectually honest person) that college has been oversold; many students floundering in college would be better served by trade schools: http://seliger.com/2017/06/16/rare-good-political-news-boost...
Not everyone should be specializing in abstract symbol manipulation.
And the all-too-common problem is that firms haven't prepared for the necessary knowledge transfer when those boomer workers do retire. If you've got a millwright who's been working in the same plant for forty years since it opened, he'll know every detail of how things work, where things don't match the schematics, what's been tried and how well that worked out. You can't just start that process when they turn in their two-weeks' notice; you've got to have somebody or somebodies working as assistants, and you've got to pay them adequately to keep them around. Nobody wants to do that.
