What, that planes are heavy and move fast?

What do you mean deliberately exploited? Given the information made available in the past 25 years, they didn't seem to plan for such engineering failure, it was more likely pure luck. I mean, crashing a plane, counting that the fuel would flow through the elevator shafts, still burning, and that it would soften the iron columns enough to make them buckle... it needs a competent team to plan that with certainty.

IIRC some the guys who hijacked the planes took flying lessons and were notoriously uninterested in takeoff and landing compared to steering, according to their instructors. They weren't very sophisticate.

I'll give you the benefit of the doubt, though. In a conspirational mindset, if it was a false flag operation (and it did help USA find support to rearrange the Middle East oil control, get rid of their old bomb stock, and a few other perks), a State certainly has the proper people to plan such scheme, and the actual hijackers would only need to know which face and height of the towers to hit, and at what angle and speed.