What, are you insane, sir(s)? The number was not six, and if I recall correctly, the majority of the hijackers were Saudi Arabian and Egyptian. Iraq had nothing to do with Al Qaeda until the US invasion of it, at which point every Islamic terrorist organization under the sun set up camp there.
This is proof enough for me that there is a serious lack of real logic and understanding present in America, and quite a few sponges who just absorb every bit of propaganda manufactured.
As for why this happened, it's a long, complicated story that I don't know the half of, and I've been studying it for years.