No they aren't, they are all part of the same decision making process. Basic Cost/Benefit /Risk Analysis.
Scenario A) maybe 70% chance the people will back us on this war. We need planes flown into buildings We pretend to be Al Qaeda and recruit some disaffected arabs. If we get caught recruiting them, we say it was a sting operation. Very little can come back on us and even if we pay for food and flying lessons etc, we can do the whole operation fro less than $100,000.
Scenario B) We make sure the buildings collapse. Maybe 75-80% chance of the people backing us. But now, as WELL as recruiting suicide pilots, we now have to rig 2 large buildings with super special silent explosives without any of the 50,000 people who work in them noticing. We can't guarantee that the planes will hit a certain floor so we will have to hedge our bets and put explosives on Many of the upper floors. We also have to somehow find a way for the explosives to not go off when hit by the plane or due to the subsequent fire until we are ready. Benefit up slightly ,. Cost now more than 10 times as expensive once we weigh in the explosives, and the time it will take for the demolition experts who need to be paid well to murder US citizens to plant all that, plus the extra effort required to do all this in secret. Risk probably 600% more likely of something going wrong or us getting caught. Especially if we also blow up a 3rd building for no discernible reason.
Scenario C ) To make sure we hit the floor we need to, instead of having a plane hit the building we have a cruise missile, with a 3D hOlographic projector on to make it LOOK like a plane. WE cut down the explosives and the time needed to plant them, BUT Cruise missiles are REALLY expensive, convincing 3D holograms are really expensive and probably don't exist, plus, as we have still got to hijack some planes anyway, we now have to find somewhere to land 4 planes, murder the 200 odd people on board and dispose of all the bodies without anyone seeing THAT.
For a tiny extra benefit, each new plan gets way more expensive, way more complicated, way more likely to go wrong,and way more likely to get caught doing it.
If YOU were the "planners", seriously which option would YOU pick?