The Towers failed as designed.
They collapsed vertically as the floor beams sagged as a result of the fire, as they sagged they came off the beam seats and fell to the floor below, exceeding the load capacity of the supporting steel and this accelerated with each floor.
The concern at the time of construction was a winter hurricane, a category 5. The fear was the tower or towers could fall like a tree and cause a domino effect up Manhattan.
Because of this fear, the floors were designed to walk off the beam seats if the buildings leaned to far off-center, preventing them from falling over. It was also assumed that they would have enough time to empty the building before the storm.
This is the first time I’ve heard they were designed to fail in this way.
The truth is, even thought their designers just weren’t evil enough to comprehend such an attack (and were thinking of hurricanes), the way they collapsed was the safest to the city so they worked.
I am sure some died in the cloud of debris but not as many as would have had the tower fallen intact.
Never thought about that before.