The real reason we haven't had another 9/11 terrorist attack.

A few dozen conspirators, probably no more than thirty or so including the 19 hijackers, spent an estimated half a million dollars to murder 2,977 people, cause billions of dollars in property damage, and provoke a response that would in turn claim hundreds of thousands of lives and cost trillions of dollars.

The remarkable thing isn't that it happened, it's that it doesn't happen more often. There are all sorts of ways a small group of people could murder thousands on the cheap... and the jobs-program security-theatre efforts of the government do very little to stop them. The TSA has not saved a single life in its entire existence, and the rest of DHS can't claim much better.

Perhaps the most reassuring fact we can take from this, seventeen years out and without anything close to a repeat occurrence, is that the number of people who actually want to commit mass murder is minuscule. The number of people who have the means to carry out such an attack is very large, but the number of people who have the requisite motives is very small. And even most of those are usually too deranged and mentally impaired to succeed at doing any better than lighting their underwear on fire.

Out of means, motive, and opportunity, it's almost entirely the lack of motive that is responsible for your risk of dying from terrorism being lower than your risk of dying in a lightning strike. That's the primary reason we haven't had another 9/11, not because the wars and the security theatre have done anything to prevent terrorist attacks.