They test the TSA with weapons and most get through. This means people don't wish to use weapons to hijack planes, or it would happen way more often and it doesn't.

It doesn't happen now, after 9/11. 9/11 was a one-time thing, and basically ruined airliner hijacking forever for other would-be hijackers. Before 9/11, people were taught to comply with hijackers because it was just a political stunt and people generally didn't get hurt. After 9/11, passengers will now fight for their lives because they'll assume the hijackers are religious kooks who intend to murder them all by flying them into a building. A few hijackers with razor blades today will be torn limb from limb by the other passengers.