[tyingq]

A fair amount of the security isn't really adding anything useful anymore. 9/11 only worked because the passengers assumed it was a hijacking, and therefore, cooperating meant they would likely live. That's out the window now. Passengers now violently subdue anyone that even seems suspicious. Between that and the secure cockpit door, a bomb is about all they have left to do anything on a large scale. Even that is tricky. The size of bomb you can sneak on limits the effectiveness[1]. Basically, the "ROI" on attacking planes isn't what it once was.

[1] Yes, you can find examples where it worked. But you can also find examples where most passengers survive even extensive damage to the aircraft, like Aloha Airlines Flight 243 (not a bomb, but still). Or Daallo Airlines Flight 159, where the bomber only killed himself.