Why don't gravitons clump together if gravity is made of them?

[wolram]

The only thing i think i know about gravity is it is an attractive pseudo force, so when one imagines gravity as gravitons, why do they not clump together and cause gravity anomalies
(gravity with no mass)?

 

[Chalnoth]

Why pseudo force instead of force?

As for gravity with gravitons, that would be because they have zero mass, and therefore move at the speed of light, which means that they tend to escape pretty much whatever gravity well they're in.

Obviously something interesting must be happening with black holes, but I'm not sure we know the details of what happens there without a quantum theory of gravity on hand.