My snark aside, you’re missing a totally other reasonable explanation. Prior to 9/11 hijackings were relatively safe affairs. They would land and negotiate for money / demands and release passengers unharmed. So sitting passively was the safest approach, Post 9/11 the cockpit is completely locked down (regulatory requirement for flights to/from US) and passengers know that any hijacking might be a suicide attacker and thus won’t sit passively. See underwear and shoe bombers as examples where bomb materials got through security but passengers subdued the attacker. That’s why US Marshals stopped flying. Attacks are too rare to warrant meaningful useful security on even a small fraction of flights.

Now arguably those were international flights into the US. You could argue that security was lax abroad but generally TSA regulations and technical requirements apply to security screenings for inbound flights so there’s not any particular reason to believe that the TSA would have done a better job.