I've always thought that the personal motives were at least as much a factor as the political goals. UBL and his inner circle defined themselves as jihadis during the resistance to the Soviet occupation of Afghanistan. When that fight ended, they needed to either find new identities or find a new jihad, the latter being the more attractive course. UBL himself went in the course of a few years from being the victorious champion of Islam to occupying a not entirely trusted desk at Bin Laden Construction, and it didn't take long before mouthing off about the royals landed him in exile. He had every imaginable personal motive for going back to his jihadi identity, and a jihadi needs a jihad.