By the time Bush spoke in NY in September 2001, the left had already ridiculed him for reading My Pet Goat through to its end; accused him of hiding out, flying around in AF 1; and , of course, refused to fly American flags at their homes because that was some sort of a right-wing thing. Revisionist history.
Bush got a lot of flak for not rushing out of the classroom right away when he was told of the attacks. (If he had, he would have been chastised for frightening the children.) He probably had an idea how quickly the Secret Service could arrange for the group to leave the school and knew that it wouldn't help anything to leave the classroom before that.