Although a death toll in excess of 5,000 is incomprehensible, the fact that there were 50,000 to 60,000 people in those buildings and another several thousand on the adjacent streets and in the concourse area below makes the death toll in New York miraculously low.
This is not a fact. No one has determined exactly how many people were in the buildings. From interviews I've seen, a number of companies while offices there had 'shifts' with later starts so the building wasn't nearly as busy as it could have been two hours later. I've seen one estimate by a company representative that "only" 20,000 may have been in the towers based on the time of day. If that's so, it would mean almost 25% are missing. Another 25% were injured.