Arkham is basically a villain factory to create anger fuel which keeps the Batman persona alive. Regular villains get re-processed every once in awhile to keep them from getting better and new ones are generated to replace dead or defunct ones. Bruce gets to keep the cycle of violence and revenge going which in turn feeds into his insanity.

I’m sure it’s not a decision anyone is consciously making. It never has been. The Bat-Spirit under Gotham has used Arkham for centuries and has stocked it and the city with crazier and crazier people and groups over the years, culminating in the current generation. It has gained enough power to manifest and free itself through the body of a young boy who fell into its cave.

Here is something else to think about. When Bruce fell perhaps he almost died but was saved by the Bat Spirit sharing itself with him......or maybe Bruce died back then and was replaced by the spirit who took up residence in his body. I could see it losing its memory and thinking it was the boy all along until years later when a bat hit Bruce’s window and woke something up........something that was hungry. And it’s food? Violence, insanity and despair.