Generational Amnesia
It was clear to me in the weeks after 9/11 that the idea of terrorism would not be eliminated by the usual tactics, and that the idea of terrorism (or the Meme), would evolve and adapt, and it still is. Once 15-20 years has passed from a major event, the generational effects begin to assert their influence, and a "generational amnesia" occurs, where memories are blunted and/or distorted from overuse (The "Mandela Effect". By that metric, 9/11 could have happened in 1949) .Those that weren't alive at the time rely on the hall of mirrors that became the media as we know it now. Social media hadn't existed yet, but morning news magazines like Good Morning America actually broke the story, in a time when you could be "glued to the TV". The fact that attention could be adhered to cognition is amazing in retrospect.