The IDEA of the TSA is to standardize all port security, not just the x-ray of your stuff and making you wait in line.
Then, somehow, they managed to make it even worse.
And airline personnel have to abide by the law since they can be taken to court. That's a VAST improvement over the unaccountable TSA.
And, oddly, the airlines actually didn't cut corners. What "needs to get caught" is well-defined, and all holy hell breaks over the heads of people if it doesn't get caught.
Now, that means that airlines train their security to recognize the test firearm rather than actual general firearms, but that's a failure to define the problem correctly rather than cutting corners.