Obama needs a victory. Somewhere. After losing congress and returning from another useless international trip, that victory has to come from somewhere. Outmaneuvered on the home front, he desperately needs to regain his stature and upstage the new Republican congress with a major achievement. And it's clear now to even his dimmest media supporters that such an achievement won't come from another international tour.
His political status as the occupant of the White House, and his own personal celebrity, mean that he can hop on Air Force One and get a reception in most countries. But having cocktail parties thrown in your honor and actually being listened to are two different things. Internationally Obama has become a "party guest", whose attendance brings status and media attention, but who isn't to be taken seriously.