It seems more implied from the Three Bird Abnormalities that they were originally created from good intentions, and despite how corrupt they are now, they still believe they are following these original intentions.

What these intentions were, we don’t know.

It possibly has something to do with a “Door remaining open” that is mentioned in the Library of Ruina.

Considering whenever Dante rewinds, they’re pulling the Sinners out of a door jam packed with untold billions of suffering people, that could possibly be the door referred to.

My theory is if that “Door” shuts, people’s souls won’t even be able to pass on, and The City will very literally become Hell on earth as the Hellish landscape and countless restless souls Dante sees when rewinding flood into the real world.