Part of bin Laden's goal is to die a martyrs death. He wants to trigger a general uprising by all Muslims against the West. Of course he doesn't want to die till he's achieved his goals, he's not going to make it easy for us but neither is he going to go away or give up.

Continually provoke the US with greater and greater acts of violence, because each greater response creates more Muslims willing to fight for him. It's a rather twisted reasoning, but logically sensible.

Jay