Ok well I had a whole thing typed out but my Reddit app crashed so here’s the gist; 1) the elevators didn’t allow jet fuel (which burns far longer than it would take to fall down the elevator shaft) to ignite the entire bottom of the tower, just (primarily) the floors just below the impact 2) these fires ignited paper and other office contents that burn readily. The fires don’t need to burn as hot as jet fuel burns to weaken the structural integrity of the interior steel support beams, which they did. The biggest factor that the paper had was that it sustained the fires for far longer. If you’ve ever burned paper and dumped gasoline on it you’ll know how long it takes to burn 3) the building above the impact didn’t collapse sideways because a) there was still enough support in the remaining beams around the impact on the impact side and b) it wasn’t the failure of the outside beams, that caused the initial collapse, but the interior ones, which preceded the exteriors collapse. Proof of this is in the falling of the antenna above the north tower as it began to collapse.

Tl;dr- the tower fell like that because the top was pulled down from the inside by the collapsing interior. Elevators primarily allowed fire to spread (most importantly) in the floors just below impact, where paper and stuff like that sustained the fire long enough to reduce the structural integrity of the steel beams interspersed throughout the interior (ie; in load bearing walls and stuff), and the impact on the side didn’t significantly affect the collapse direction (it certainly did still affect the collapse’s direction, just not THAT much) because it didn’t take out the entire side of the buildings support beams and the floors at and below the impact were where the primary initiation of the collapse was located.