The people who like to manipulate us by creating and preserving anger like to give us slogans. Remember the Maine, Remember the Alamo, Remember Pearl Harbor, remember the raisin! Never Forget!!
All these things are inevitably forgotten despite the slogan advertising campaigns and sooner or later we'll get tired of remembering 9/11. Sloganeers will get tired of milking the faded fear and self-pity and choreographed mourning. The people who were born too late to remember it will eventually need to be told to remember something else that some party needs to cultivate anger about, so as to pass some kind of horror like the Immigration and Nationality Act of 1952 or the Patriot Act. 9/11 will be forgotten by most everyone but historians and those who remember will remember it in context of the things we did and the laws we passed and the freedom we gave up while we were whipped into a passion.
Think calls to 'always remember' are genuine and untainted by politics? Wonder why we shouted Remember Hoover! in 1936 but nobody remembers to Remember Bush? Remember Katrina and at least 1800 fatalities? Why not? We spent billions and billions on a the Largest government agency in history and abridged the Bill of Rights in 2001, but we didn't do a damned thing to improve reactions to natural disasters which you can be sure will occur more often than a repeat of 9/11.
I suspect that calls to remember are calls to preserve a mental state in which we can be manipulated, tricked and sold some unsavory product. Stay angry, stay afraid and obey.