It's a cultural thing to a degree, but it's mainly due to the fact that you have a bunch of very wealthy players (oil) in that world who have nothing better to do but agitate and enable hate and discontent. Of course they pull strings from the shadows, rarely participating directly in terrorism...UBL was a notable exception, but for every hands-on guy like him there are a hundred who prefer the comfort and safety of their air conditioned compounds. But they write a lot of checks.
There is a large and recently expanding network of madrassas over there which deal in hard-core islam, providing the base ingredient of "committed" young men.