A repeat of the 9/11 attack became impossible before that day was over. It relied on the passengers and crew cooperating with the hijackers until it was too lat

A repeat of the 9/11 attack became impossible before that day was over. It relied on the passengers and crew cooperating with the hijackers until it was too late: they would think that the plane is being diverted or held for ransom and the safest thing to do would be to go along, because that's how hijacking worked from the 60s through the 90s. But now everyone knows about 9/11, so everyone will fight like hell to prevent the plane from being taken over, because the assumption has become that if the bad guys get control everyone will die, and if the hijackers claim otherwise no one believes that. The bad guys know this: they figure an attempt to do a 9/11-style hijacking will result in failure and death without doing damage to anything but the plane itself. No flying into the Capitol or the Pentagon in a blaze of glory.