It wasn't just oil, the reasons were laid out by PNAC in their document arguing for the US to benefit from a Middle Eastern war in the Middle East and their letter to Clinton pushing him to use force against Saddam. Bush's name was on the Oval Office, but PNAC was the government, pretty much.
Yes, there was a big motive - the political success of both the Bush Presidency and the right-wing agenda.
But the conspiratorial question it might raise is whether the Bush administration thought that letting the terrorists get an attack on America they could rally around, just as the US public had been against entering WWII until Pearl Harbor - the PNAC people themselves said earlier that a 'Pearl Harbor-like incident' would be the best way for them to accelerate their desire for the US to use force in the Middle East - and they relaxed the measures to prevent an attack for that reason. It's a far cry from planting explosives.
A poster asked the question, if they planted explosives, why fly planes into the buildings?
I think that's backwards; if they were part of a conspiracy to not do much about the planes flying into the building, whether or not aware of the plot, why jeopardize their whole movement to become the most treasonous in history with the risk of getting caught for a conspiracy themselves to plant explosives, when the the 'benefit' of the attack for them was done with just the plan attacks and the explosives added largely nothing?
I'd rather someone care about the issue and get it wrong, like Kyle IMO, than someone ignorantly not care and just say there's nothing to it and let the government be able to do something like that without getting caught, which invites it to do more and more things it thinks it can get away with. But that's not to say I don't think Kyle goes beyond that into one who unfortunately makes big errors in buying into the wrong theories.