The movie was not about 9/11
Perhaps the writers and film makers felt that the movie was really about 9/11, but in that case it would have to tell us something about the event. If the movie was instead about how everything we love can disappear in a moment, then you don't need 9/11, you just need an auto accident or something that happens to a lot more people.
If it was supposed to be about 9/11, it should have explained why so many people felt that it was worth dying for just to send us a message. Now that would be a useful thing because most Americans have no interest in understanding why so many people hate us so much. They are even proud about not knowing. That was a teachable moment. The only thing that this movie taught me about 9/11 was that it happened on a Tuesday.