Airport checkpoint security was the ONLY link in the entire chain that DID NOT fail on 9/11. The bad guys were let through with items that were APPROVED at the time.
The FAILURES of 9/11 were : FBI, Immigration, Local Flight Schools (to a point), and the Airlines themselves at the ticket counter.
SECURITY (checkpoint) WAS NEVER BRERACHED ON 9/11!!
So what do we do? We change the only part of the system that actually "worked" and leave the other major problems completely alone or throw superficial "fixes" at them.
Welcome to knee-jerk America folks ...