Because:
The Peter Principle is a management concept stating that in a hierarchical organization, employees tend to be promoted based on their success in current roles rather than their aptitude for higher ones. Consequently, workers are repeatedly promoted until they reach a position where they are no longer competent—their "level of incompetence".
Because an employee's competence in their baseline job is celebrated with advancement, this cycle continues indefinitely. However, the skills required for a lower-level job rarely match the demands of an advanced or managerial position. Once the individual reaches a role that exceeds their specific capabilities, their performance drops, and further promotions stop, trapping them on "Peter's plateau".
Over time, this flawed promotional process leads to widespread organizational inefficiency, as many essential posts become occupied by incapable individuals. To counter this, companies often need to reassess how they define success, evaluate leadership potential over technical skill, and create parallel career paths that reward experts without forcing them into management.