In "The Devil's Hands Are Idle Playthings", the Robot Devil loses his arms, he never can lay his hands on Bender's soul for lots of reasons, such as redemption (Ghost in the Machines), sacrificing his first born (Beast with a Billion Backs), etc. My guess would be that the God Robot has a certain beef with him, thus always turning things against him, probably because his god-awful music bits. :D
So: is it explained at any point in the series why Robot Devil is so unlucky? Is there some force working against him? Was he slated as the fall guy for some out-of-story reason?