I also found a magic rock that keeps away tigers. Would you like to purchase it? No tigers have ever been spotted in my area since I found it.

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.

The biggest thing that stopped 9/11 attacks since 9/11 was locks on cockpit doors.

The second biggest thing that stopped them since 9/11 is passenger awareness that they could just... Not let a few assholes with boxcutters fly a plane into a building.

There also wasn’t a 9/11 before the 9/11.

Securing cockpit doors is what prevents the next 9/11. It was both necessary and sufficient.

The end of 9/11 happening again occured right in the middle of 9/11, with UAL 93.

Passengers figure out it's not a hijacking they might survive, and that you're going to crash the plane into a valuable target. Then, having nothing to lose, they revolt and ruin your plan.

So that particular type of plan isn't going to work again. Passengers no longer assume "hijacking I might survive".

I am also not aware, in the history of aviation, of a terrorist attack that was stopped at an airport security check.

Edit: <not worth engaging>