They really could not see any advantage to going along with such a brash deal. It took much pressure from the new U.S. leaders, the blandishment of billions of U.S. dollars in "fees", and the personal assurance of George Tenant, the C.I.A. Director that nuclear weapons would be found in Iraq to cover the operation, to get the Saudi rulers to allow the bin Laden family to begin the negotiations, with Osama, for the attack on the U.S. This would be the "Pearl Harbor" type attack that neo conservative doctrine called for, in their plans.
The U.S. Administration agreed that Osama would be protected in the ensuing war and would be assured safe haven in Pakistan. The U.S. also agreed that the bin Laden family would be granted free passage, in the U.S. and Pakistan, in the immediate aftermath of the attack.
Now, 15 years after the attack, the Saudis, who played a relatively minor role, is facing major liability claims, in the U.S. for abetting a rogue operation of the then U.S. government, while the master minds are now peacefully retired as well as enormously rich.