The airport structure is build for the transport of citizens. Airlines make the profit. If they're held responsible, they'll solve the problem.
What do the airlines have to do with it?
The TSA does the hiring. Airlines may or may not make a profit. If you want to fine them for employees they don't control, how is that going to change their behavior?
You might as well fine General Motors for every theft at the airport. It makes as much sense.