There _was_ a conspiracy: a group of Islamist terrorists conspired to attack America, and (unfortunately) succeeded in killing thousands of people. Why the kooks have to find a _different_ conspiracy is a mystery to me.
Exactly, but they do it with every big event. It's like worms breaking up out of the earth and crawling around, after a heavy rain. There are always conspiracy theorists. World class jerks like Michael Moore make big bucks at the conspiracy game.