I am forced to take issue with your premise -- there have been
numerous attacks, and known attempted attacks, since then. Most of the more successful have been overseas, such as the London Underground, the Bali bombing, Spain, etc., but this is in no way inconsistent with bin Laden's stated goals or
modus operandi.
If you are asking me to speculate, I would have to guess the reason is manifold:
- bin Laden did achieve many of his stated goals, such as striking at the American heartland and embroiling the US in wars overseas
- His operations are redirected towards keeping us involved in overseas wars, rather than having to start it all over again
- Military operations and capture of confederates has limited his ability to plan, his assets, and his access to funds
- More recently, it has become increasingly clear that Islamic scholars and community leaders are visibly rejecting his techniques, even in the most embattled areas
- He also might simply be retooling -- either focusing energy on an even bigger score (though I have no evidence of this) or suffering the usual middle-management revolt that inevitably strikes any organization after enough time
Could you be more specific? What do you think it means? I don't see anything out of the ordinary at all.