Other factors may include
"can't earn more unless you become a manager syndrome".
No good post made available after the latest reorganisation - always tempting to eliminate senior posts rather than junior ones to save money
I don't know about corporate IT. But in education that holds true, definitely.
And we also have a truly diabolical combination of Peter Principle (good teachers and departmental heads being promoted out of the classroom to managerial jobs they're useless at) and ambitious young climbers who plot their way to the top asap by jumping on every initiative and new programme that comes in, and adroitly moving on and up before it flops ( they all flop)
Which means there are a lot of experienced, effective, good, jaded, frustrated middle aged teachers who can't wait to get out and retire as early as they can. And managers who want them to, to save money and appoint cheaper staff that will be amenable to whatever new best thing bollocks they're being asked to take on.