If you aren't moving to another job every 2-3 years, you aren't getting paid what you are worth. Job hopping provides faster raises than any smoke and mirrors cost of living "calculations". Working a multitude of different jobs makes one more well rounded with exposure to more varieties of equipment.
I've worked in industrial maintenance jobs that had ancient hard wire relay logic and AB SLC-500 PLCs. AB stopped supporting that platform many years ago. Spare parts are on Ebay if you are lucky. If that company laid off any of its 20+ year maintenance employees, they would be worthless in any other modern manufacturing facility because they had no exposure to the latest and greatest tech.
I've never left a job because the work was too hard. It's always bad management that runs the best and brightest off. Those kind of companies are stuck with 20+ year employees simply because they can't find a job anywhere else.
I'm currently working with about a half dozen guys that say they're too old to learn how to use a diagnostic laptop or to learn electrical troubleshooting that involves more than a test light. Half can't even use a test light. It's basically a fucking retirement home on one end of the shop but management caters to them. They have no retirement and will be here until they die. Like you said, they can't go anywhere else because they are too far behind the times.