Conjecture: the bin Ladin strike force is in motion now. We may not be able to prove he did this, but he's done it before and no one will be able to raise a legitimate complaint if he's snuffed out without a direct link to this crime. The problem will be collateral damage and innocent casualties. If those happen, especially without proof positive of his involvement in this case, that will be a problem. So maybe bin Ladin is already shielding himself among many innocents, perhaps with hostages, so to speak, who aren't harboring him or aiding him - relative innocents.
next concern: does bin Ladin have a 'last will and testament'? If he is killed, do contingency plans go into effect?