This has been known forever, yet it still happens - Why?
>> I'd much prefer putting younger managers with great management skills into the mix...
One reason is it is impossible to tell if a young manager has great management skills. It's really hard to tell if an experienced manager has strong skills.
As a result, technical proficiency is used as a proxy for management potential. It probably has a stronger correlation than picking a random person, but is not great. The new manager is then really unhappy, quits or is fired or eventually learns the new skills and is successful.
Repeat.