The Peter principle is a concept in management […] which observes that 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
This phenomenon is very visible in creative departments, as creative professionals get promotions towards management for their individual contributions. This is how the best designers end up as shitty managers.