This is based on a small knowledge of the physical situation (the WTC towers were like a stack of bicycle wheels, with steel beams for spokes, and the floors held up by those beams) and the effort to answer this question: what would motivate me to jump into freefall, when I don't believe in suicide?
(steely)
I think the office workers were 'pushed' out as well, when the plane went into the towers.
What a terrible choice to have to make.