Money? Easy, they're in charge they make the rules, they can easily change them to benefit themselves, family etc, plus they are generally the ones with money in the first place.
Power? What, more power?
War? Really? They want war? Again, why?
Just for the hell of it??
I've asked this question of many, many conspiracy theorists and not one has come up with a good enough answer. I put the question to you all now.
What happened that day was some nutjobs managed to get past (pretty lax) security and onto planes, nobody had considered such a simple plan before and what did they have against them? One of the most simple minded Presidents the world has seen. A simple plan, carried out with catastrophic consequences, not just for the poor souls in NY and the Pentagon but also the other hundreds of thousands killed since.