Bane thought that the barriers in Patrick Bateman's own mind would keep him from ever escaping, and, frankly, it was a total asspull that in the end he suddenly was able to get a hold of himself and climb out when the work he's originally from is all about how him not being able to get a hold of himself without changing something fundamental within himself. It's not even like the post-credit scenes do anything at all to establish any kind of character development like that. Bateman just dicks around in cameo scenes, then he suddenly gets pulled into the plot with Bane and Nolan's suddenly trying to make him a main character, then suddenly Nolan's written himself into a corner and he has to pull asspull after asspull to keep the script going from where he's taken it.