>Expert machinists using fancy equipment in a factory don’t really have the same ability to just go to a competitor, so they can’t negotiate a raise.

Machinists own their own tools, in general... and I knew a CNC machinist who quit, went somewhere else, and came back to the shop I was working in over the course of a few months... they aren't easy to replace, even in a job shop. The equipment is a sunk cost, and if you don't have someone who knows how to use it, you're wasting money while it's idle.