I guess the underlying reason is that engineers wont be promoted to (real) chief engineers with agency. Being a boss requires reports for some reason. So experienced people leave sweetshops to escape the grind when they get fed up.
Sadly, this is absolutely true. Manage or be managed. Capitalism invariably becomes corporate (if unchecked, monopoly) capitalism which invariably becomes managerial capitalism, in which people are assessed by their position in the tree structure rather than anything they do, and 0 reports |= loser.
Unfortunately, if you think you can take on a middle-management role and also do technical work, you're probably wrong. Middle management isn't hard but it's super time-consuming, if you do it right (that is, if you care at all about the people you're managing, although you won't have much ability to protect them as you might hope for, because PMs). You'll barely know what the people under you are doing (most managers'll admit this in private) because so much of your time will be spent on meetings and political bullshit.
Big tech that I work at generally doesn't have MBA type managers and it is good.