Berserker

A berserker is a hypothetical type-5 entity that waits for other, weaker entities to reach a sufficient type. After this, they will come and destroy them before they can advance further. The concept that Berserker exists is called Berserker Hypothesis, which gives a reason to believe there are no entities outside of our local planet.

Great filters
Main article: Great filter

A similar idea is that there is an action that makes almost all entities self-destruct after they advance to a said type. This is called a great filter. One great filter could be that life has extremely strict requirements, but this is unlikely to be true.