I already worked for companies where there were management changes at a crazy pace, I'm not sure that all of them got promoted and I have the impression that some of them might have been fired as well.

I don't want to start a flame war but it's much easier to replace a manager than a technical person, a technical job is boring and most people don't want to do it while management relies more on soft skills, something that most people can do at a minimum level. Being a manager who's always employed is more about social connections, if you don't befriend the right people your job security might also be at risk.