What are the main reasons why academics leave academia? (Looking for references, not personal opinions)
I retired immediately after completing my Ph.D., but would have switched back to industry if I had continued working.

I am much, much happier and more effective doing technical work than teaching or managing. The computer industry has well-established technical tracks that allow career advancement without becoming a manager. The academic world, at least in the USA, seems to require teaching and administrative work from everyone, regardless of individual preferences and talents.