My related take in this is that airports are expensive to maintain because you waste a ton of space on vendors and seating areas. If airports were just shacks next to a runway, they’d be much cheaper to run.
So you can’t really charge people for sitting/waiting (though the private clubs sort of do just that). Then you charge people for the other purpose (rent on vendors) and that pays for everything.
But you can’t tell your customers “it’s actually really expensive to build these giant buildings to just hold CIBOs and Dufry” since they won’t believe you (or worse call for smaller more efficient airports to be built with fewer services).
So you just sort of play this very bizarre merchandising game.