Probably because Biden is a brain dead fool.
Via Vanity Fair:
Bowden contradicts reports that many of the president’s top advisers opposed the raid. “Nearly everyone present favored it,” he writes. “The only major dissenters were Biden and Gates, and before the raid was launched, Gates would change his mind.” According to Bowden, Leon Panetta told Obama that he ought to ask himself this question: “What would the average American say if he knew we had the best chance of getting bin Laden since Tora Bora and we didn’t take a shot?”
Only Biden would be dumb enough to oppose such an easy call.