What am I missing?

[SelfGovernor]

Turnabout is fair play

TSA is not required to actively search for CA illegal items but if it is discovered during a federal search they are obligated to alert local LEO. TSA has helped bust abalone poachers in CA among other CA related violations. There was a big child porn bust at SFO years ago. While not something that could fly a plane into a building it was still illegal on federal and state levels.
Gun mags are not a federal issue and do not have a negative impact at the state level so a pro-2a tsa employee could easily overlook it. Just like local leo often overlook switchblades. The paperwork is not worth it to them.

Since the 2A infringing states tend to be "Sanctuary" states, what if there was, let's say, an executive order that all Fed LEO will look the other way on state gun laws...

SG