Fine, though I presuppose you will refuse to budge from your "inside job" (which is a 100% impossibility, BTW) thinking.Each of the Twin Towers, nor any large fraction of the buildings, was not an "object" insofar as you are pretending to argue. Your wish to appeal to "common sense" that 1/10 is smaller than 9/10, therefore making it such that it "never" could happen is flawed on its face. Try not to view the Twins as they were from afar, but rather inside their walls.
Also, any building is not a static object; it is, by successful design, winning the struggle against the constant and immense force of gravity. This is true whether the building is under construction, or hundreds of years completed. They are built to a safety standard, but if that is exceeded, as it would be when such a large load as an upper portion collapses on successive support structures, the entirely expected happens.
An example you may have read in these forums: Go to the gym and lift a weighted barbell over your head, the heaviest you can manage. Let's say it's 175 lbs. Now imagine holding the same aloft with a broken wrist.
Lastly, I notice your use of "gravity alone." You wouldn't be trying to minimize such a powerful force, would you?