How can you count events that never happened? Especially if they were deterred from even being attempted by the existence of TSA alone.

Do you think a government agency would just publicly blast all the unsuccessful attempts that were prevented, without fear that future criminals can look at those attempts and do better next time by learning how to avoid making the same mistakes?

Disclaimer: I agree with most of the posters that TSA is mostly just a security theater. But just because I think so, that doesn't make the flawed parent argument any better.

There's a gulf between publishing some basic statistics and blasting the specific details of all unsuccessful terrorist attacks that were thwarted.

Surely those statistics can be verified by, say, the House Committee on Homeland Security without needing to leak the details of specific attempts.