those terrible managers realize they're shit at their new position and hide the fact by keeping garbage employees on as a cover, while pushing the people who are actually good at their jobs extra hard so they still keep their numbers in an 'acceptable' range that keeps the hire ups off their asses.

It's been a while since I've heard anyone invoke the "Peter Principle," "people in a hierarchy tend to rise to 'a level of respective incompetence': employees are promoted based on their success in previous jobs until they reach a level at which they are no longer competent, as skills in one job do not necessarily translate to another."