To wipe the royal wedding off the news cycle, because Obama wasn't invited. The I-Me-My-Narcissist excuse.
Sorry, nice dig, but too short-sighted, and it underestimates the size of that narcissistic ego, whose fortunes all hinge on race. If Obama suddenly appeared white, it would all be over in an instant.
Re-election is the goal. Ending the war in Afghanistan is the one obstacle he can still affect. The end of "bin Laden," who may well have died long ago, leads easily to closure of that debacle. Alexander the Great might have concluded as much, who got bogged down and fought until he was tired, and needed to move on.
So find a victory, declare it, and get the hell out.
The original plan had called for the first withdrawals, after the ramp-up, "the surge," to begin this summer. The "bin Laden" victory in May provides the necessary praeparatio to start them. Ending America's longest war "successfully" will make Obama popular with the troops and with the people, who all are weary.