There's downsides to the companies, though. Interviewing new candidates takes money, and takes time away from people already on the team. If everyone is switching jobs to get a higher salary, then companies aren't saving anything in the long run. They also have a major knowledge base walking out the door, and that's hard to quantify.

It's a false savings.

If I were to steel man this, it'd be cross-pollination. Old employees get set in their ways and tend to put up with the problems. They've simply integrated ways to work around problems in their workflow. New people bring in new ideas, and also point out how broken certain things are and then agitate for change.

This, I think, doesn't totally sink the idea of the "company man" who sticks around for decades. It means there should be a healthy mix.