Well, certainly OBL is the cleverest criminal ever. It's harder to find a more wanted man than he-- by the world's largest superpower-- and yet, he is still a free man-- who exercises his freedoms frequently enough. It doesn't even matter how he manages it (co-operation from millions of Islamists around the world), because the fact is that he pulled off the biggest crime in American history and he is laughing his ass off in freedom.
The reality is "time" was on UBL (and Zawahiri, M. Omar and several other HVTs) side in the short run (to avoid being captured / killed) because of the region of the world where they have ekked out their survival - The Afghan / Pak border region -
That variable (time) is now slowly turning back in our favor - But the simply reality is they survived in a region of the world that is autonomous (for the most part) to any centralized Gov't, where tribal leaders and warlords run the show (where outsiders are quickly spotted and despised) and the terrain is the most brutal on earth. The Afghan / Pakistan border (alone) stretches 1,500 miles—roughly the distance from Washington, D.C., to Denver (the complete Pakistan border is more then 2,000 miles....much of it in completely lawless regions...that have been that way for well over a century).
Trying to run sustained operations in this region at times is almost impossible. The logistics alone are a nightmare.
All these variables add up to why UBL remains alive and why time was on his side in the short run. But he is being systematically encircled and he is far from laughing his as$ off. He has seen over 3/4 of his senior leadership killed or captured, thousands and thousands of foot-soldiers killed, his cause has suffered one strategic defeat after another (while we have not suffered one).
We have brave warriors hunting his as$ (and other HVTs) risking their lives 24/7 to nail these SOB's (and they will).