One of the members of the Professional Body that I belong to did a survey some years ago. It involved working with some airports; they did not view SLF as their "customers" so really couldn't care much about them. They saw their customers as the shopkeepers and airlines.
Says it all, really
The thing is, in a business sense that is correct. Passengers in most cases do not directly pay the airports - the airlines and the shopkeepers do, and they then recoup their costs by selling their services/products on to the SLF. The only direct payment for most pax to the airport is car-parking, although that is also often contracted out to a third party.