from my research I'd say it depends on who and what level they're at. at the very highest levels of the cabal/illuminati it's ALL about depopulation and their satanic beliefs. and I don't mean depopulation by killing a few people in the towers. I mean by initiating even more restrictive controls (e.g., Patriot Act) that are ultimately intended to result in significantly more deaths than births.

now if you look at the level of say higher up in the CIA, FBI, NSA, DOD, etc, they were likely doing it for their own interior motives of power and backroom financial incentives.

when you consider the owner of the twin towers, Silverstein, he had buildings that were crap and needed to be gutted. he worked incredibly hard just before the "attacks" to secure insurance policies that interestingly enough would pay out 2 separate claims if 2 separate incidents were the cause of each collapsing. guy must be a psychic right? anyway, he had clear financial incentives to be involved in this happening