Because the real enemy of Al Qaeda, what really what burns them up the most, isnt the US. Its the autocratic governments in Saudi Arabia and Egypt both of which are friendly to the US. Most of the leadership are exiles from their own countries. Ayman al-Zawahari was exiled from Egypt for his radicalism (he was involved in the Anwar Sadat Assasination) and Bin Laden has had a decade running feud with the Royal Saud Family over a variety of issues both religious and political.
What al-Qaeda wants to do is overthrow these governments and install a 13th centure Caphilate in its place. The trouble is that since these countries are allied to the United States, the US stands a roadblock to their plans, which is why they target us. They dont like us, but ultimately its not us their main enemy.
I have seen people like bin Laden (Saudi Aristocracy) in Paris, they are the ultimate snobs. They view those beneath them as somewhere in between a turd and a cockaroach. I honest think the people like Bin Laden care even less about the Palestineans then the Isrealis do. Thats why I do not believe for a second he is sincere about wanting to help them, he is using them like Saddam used them to further his own aims.
If what you say is true, why haven't we seen more attempts of terrorism on a grand scale in Saudi Arabia.
The last thing of any real significance to occur there was the attempted seizure of the grand Mosque in 1979 led by Juhaiman Al Utaibi. Nearly all of the casualties from that were as a result of the ensuing battles by the authorities to regain the Mosque. This was more of an internal faction fight than a part of any world wide terrorist cell. The old families and factions of the Arabian peninsula have been doing similar things for centuries, as seem more recently when there was an almost farcical attempt on the life of Prince Mohammad, prior to which was the assasination by Prince Faisal of his uncle in 1975. Neither of which could be said to be serious terrorist attacks on the scale of the attacks and attempts made on the US in recent years.
Al Quaeda is a fundamentalist Muslim faction who have played the anti Infidel card using the example of our support of the Israelis to prove their legitimacy in the Muslim world, without which they would be no more than just another small and relatively unknown group of religious fanatics barking at the moon.
As such, 99% of the Muslim world couldn't give a stuff for them, there's several of these radical groups in every small Muslim town, but what has set Al Qaeda apart is the they have focused the Muslim worlds attention on their opposition to our support of Israel.
Whereas the Taliban was essentially Afghanistan centric, and having seen how Al Qaeda had played their cards, they gained notoriety and support of the more incendiary Mullahs by tagging onto Al Quaeda's shirt tails. Having a cause is not always enough, you must gain popular support to get any real recognition. Palestine is the key to the lock for them,.... and us. The trouble is, that we are turning the key the wrong way.
What do you think would happen to Al Qaeda's popularity among it's present followers, if tomorrow they announced support for the Israeli peace plan? They would immediately revert to just being another group of radicals with extremely limited local support.
The sad fact is that we have bought this on ourselves and we feel that we can overcome it with brute force. Unfortunately all our dealings with the Muslim world have taught us almost nothing of their nature. Muslim fundamentalism has been around since Muhammad first delivered the message of Allah,.... and it ain't gunna stop any time soon.