The person(s) on the top of the hierarchy, wishing to remain in power forever, chooses their associates with the prime criterion of incompetence; they must not be competent enough to remove the leader from power.
[1] Removing those powerful cadres breaks up the networks of loyalty that could threaten the leader.
Emptied positions in the hierarchy are normally filled with people from below—those who were less competent than their previous leaders.
Once the leader dies, or is removed by an external force, what remains is a grossly ineffective hierarchy.
In a famous anecdote from Herodotus's Histories, a messenger from Periander asks Thrasybulus for advice on ruling.