Yes ... people are forgetting about 9/11, especially those not affected.
It's been about 25 years since someone born back then could really remember it in any reasonable way (think 18 years ago plus the child was 7 at the time). Unless people are directly affected, they forget things over time.
Think of the Vietnam War, Korean War, WWII, etc. As time passes, things are forgotten or at least delegated to a part of our psyche that finds little relevance of the event(s) in our everyday lives.
Rub a Dub