Certain villains in the Batman's Rogue's gallery like Two-Face, Penguin, Riddler, Joker, Scarecrow, etc that feel THEY are the number one and they wouldn't cross Joker anymore than Joker should cross them or they should cross each other.
I'm not saying they shouldn't cross each other at time, just that it's usually more trouble than it's worth and not something they should go out of their way to do except in special circumstances.