Everyone was thinking "it was a controlled demolition" or talking about Lazer beams, trying to explain that the plane was edited in, maybe the towers never even existed and were invented by the media. But in reality it was a lot simpler, the Saudis sent people to fly planes into towers. Was the "jet fuel can't melt steel beams", like, purposeful misdirection or were conspiracy theorists just too imaginative for their own good
I always interpreted as two things, since this was one of the rare instances where libs (mostly radlibs) and conservatives both somehow adopted the same conspiracy theory. I've hung around a lot of conspiracy theory circles and there are strikingly few groups that have mixed political ideology. For the libs, I think it was a way to further demonize Bush and express an anti-war sentiment, since they didn't have any kind of structural theory to explain American imperialism. For conservatives, it's a way of protecting American exceptionalism while at the same time expressing that very odd sort of "antiestablishment" Alex Jones style brainworms. It's a way of saying America is so great there could never be a legitimate external threat while also expressing a distrust of the current internal structure.
in essence, it's alienation, brainworms, and an inability to place blame on imperialism for anything. It's literally easier for Americans to accept the government would create hologram planes than accept America gave $40 billion to the mujaheddin so they could become Al-Qaeda.