By the nature of the damage, assuming you believe, as I do, that the damage was caused by aircraft full of fuel flown into the structures, it is reasonable that the towers collapsed into their own footprints. The towers were damaged not at, but near their tops, creating severe structural damage that would have supported the remainder of the buildings had not the heat of burning fuel, paperwork, furniture, plastics critically weakened the structural steel that remained. This left the intact part of the structure overhead like a big hunk of mass ready to start dropping down on the 'layercake' structure of suspended concrete floors. The lower part of the structure and its foundations were intact until the very end, forming a kind of supported tube within which the failure occurred. Once the big mass at the top tore loose, I suppose it might have veered a bit to one side or the other, but the floors below had basically one way to go - straight down.

Remember that the second tower was hit lower down, leaving a bigger mass up top to hold up with the diminishing strength of the steel supports. The failure occurred ahead of the tower which had been hit first, only higher up.

The 1993 big bomb in the parking garage, had it been bigger, as Ramzy Yusef said afterwards, might have resulted in a very different collapse footprint.