Let me explain then.
Osama was the CIA's jihad recruiter in the 80's, code name Tim Osman, seen here in Pakistani uniform showing jihadi weapons to Jimmy Carter's national security adviser Brzezinski, a rabidly anticommunist Polish aristocrat who was the original author of the whole anti-Soviet jihad shindig, from Afghanistan to bringing Khomeini to Iran.
The Soviets saw, as NATO sees today, that no amount of troops could subdue the warrior tribes of Afghanistan, and conceded defeat, leaving behind a nominally socialist government allied with Uzbek and Tajik tribes, the same ones that the Yanks used to chase out the Taliban in 2001. After the Soviet retreat in 1989, the Yanks decided to pull the plug on the jihadis, both in Pakistan and among the Arabs in Afghanistan. They started by assassinating Pak dictator Zia and his head of the Inter-Services Intelligence, both of them jihadi fanatics. The new Yank-appointed ISI chief ordered the jihadis in Afghanistan to mount a frontal assault on heavily-defended Jalalabad, over a totally exposed plain. To maximise jihadi casualties, the CIA blew up their arms depot in Pakistan and sent them no new supplies through the winter of 1988-89.
Osama was wounded at Jalalabad and saw many of his friends die needlessly. He put two and two together and realized that his bosses had betrayed him. So he started using the CIA's rolodex of jihadi terrorists to get back at the US. The CIA name for that jihad database, used both in Afghanistan, Bosnia, and Chechnya to achieve Yank strategic purposes, was "al Qaeda," which means "the database" or "the registry."
The Yanks never wanted to kill or capture Osama. They were in constant contact with what they apparently saw as a temporarily rogue agent who could once again become a valuable asset. Gaddafi put out an Interpol red bulletin for Osama's arrest, the Yanks quashed it. Sudan offered to hand him over, the Yanks refused. Osama sought refuge among the Taliban and the Yanks continued to invite the Talibs to the US and treat them like royalty. Two months before 9-11, the CIA station chief in Dubai visited Osama in a hospital.
Meanwhile, a guy called Mohammed Atta with links to Syrian intelligence was being wired $100,000 by the head of the Pakistani ISI. Soon after, a Mumbai-style commando with Syrian-style plane hijacking expertise pulled off a major terrorist operation against the Twin Towers and Pentagon with the full knowledge of Israeli intelligence, which had tracked the terrorists' every move, and that of the Yanks, who took great pains to quash FBI investigations against the terrorists-to-be, turned a blind eye to their outrageous visa violations, and stood down their air defenses, yet they hardened the section of the Pentagon - and only that one - that the terrorists would hit so as to minimize the damage.
When the terrorist attack was over, the Bush cabal started thinking about who to pin it on. Wolfowitz, Perle, and Rumsfeld adamantly wanted to blame it on Saddam so as to invade Iraq, something that they had been campaigning for over the past decade. Bush and his Texas oilie buddies had other ideas, however. They had been trying to close a pipeline deal with the Taliban for years and had just served the Talibs with an ultimatum: Sign up for the pipeline and receive a carpet of gold or refuse and receive a carpet of bombs. The Talibs told them to stuff it. The Pakistani foreign minister who atended the UN-sponsored Berlin meetings with the Taliban, told the press that the Yanks were going to war "before the first snows." In October 2001, they did just that.
Osama was again allowed to roam freely as Yank AWACS radars tracked his convoy in the heat of the invasion. At Tora Bora, the Yanks left the back door open so he could escape to Pakistan. And today, their killer drones blow away one Taliban leader after another but Osama remains untouched.