Oh, they know. They (and supposedly, customers) just don’t want to pay for it.
Every system is testable, and more complex systems require more complicated tests and personnel that are capable of doing them:additional costs. The question of what is needed is not the choosing factor, but what is profitable. It is more profitable to use computerized systems if you don’t pay people to test them.
Just as it is more profitable to industrialize farms if you don’t pay people to take care of the land and animals.
The money spent on TSA is money that should be spent on aircraft maintenance and safety procedures for aviation, not as a bandaid for consumptive politics and human degradation.
But then, nobody wants to pay to fix that, either.
Free market economics is mostly about making maximum short term profits with systems that don’t pay for the value of resources received, while convincing the masses that any other way is 'evil’.