Sorry Charlie, but you are the one who seems to be missing something and not really understanding things here.
A natural gravity collapse would require deceleration of the upper section. This is seen in every single Verinage demolition, where one can actually say the upper section is causing the collapse of the lower section while being destroyed itself due to the equal and opposite forces involved.
However, the measurements of the descent of the upper section of WTC 1 show it never decelerates, so you have no mechanism for a natural gravity driven collapse of the lower structure which is designed to take several times the load above it.