It may not be true in organizations in which you have worked. In businesses that must make a profit, there is only a limited amount of time that a bad supervisor will remain in a supervisory position. Usually they "leave to seek additional opportunities" but occasionally they are found "a more appropriate position for their skills" somewhere else in the organization.

The last thing that will happen is that they are left in a position that will cost the employer time and money.

They are either gone or they disappear within the organization.