Anecdotally I've seen it quite a few times. In most cases, mentorship and the environment play a role in how successful you can be as an IC versus as a manager,

Anecdotally I've seen it quite a few times. In most cases, mentorship and the environment play a role in how successful you can be as an IC versus as a manager, and even within the same organization, the IC culture versus the Management culture can be drastically different and one or the other might not set you up for success. That said, in my experience when there is a mass exodus of the kind you talk about, the underlying symptom is some flavor of poor management and toxic culture. Doesn't matter if that organization incidentally happens to implement something which would otherwise qualify as "best practices of management" - in that environment it is simply putting lipstick on a pig.