How many horse farriers have you met? How many coopers, blacksmiths, or shoemakers?
How much did a horse farrier have to learn if they switched their employers?
Cobblers design, make and repair shoes of various kinds, boots for various purposes, slippers and moccasins with leather, cloth, rubber, and many kinds of threads using punches, knives, various machines, glues…
How much does a developer need to learn about their core competency when switching employers? Not even close to as much as a machinist. It’s not a useful comparison.
That is precisely the point. They still exist, but it is a far less common occupation than it once was.
> Has it ever been?
Well… yes? So very many industries shrank, even disappeared in practical terms, because efficiency, automation and technological improvements. Industrial revolution? Calculators? Computerized accounting? I mean the list is giant.
So there will always be a point where people aren't willing to hire more software developers because there are enough already.