Also, it's likely a majority of their drop-offs and pick-ups aren't even people renting cars! Instead, they're locals, who've dropped off their car at a remote lot for maybe-renting. Why should such a person be routed out through the remote rental-counter-center, when they're not a car-renter? They're most like any other local arriving via cab or limo, so that's the airport-usage-fee that should apply.
It's the same kind of un-scoped reason that leads to conclusions like trickle down theory. They think because they're proving a service that someone can presumably benefit from, that gives them a blank check to consume as much as they can to provide that service, thus completely negating the positive impact of their business through crock-pot philosophy. Obviously, there is no sound logic in this line of reasoning. Obviously, they're not going to argue that they should pay more since they don't have a fleet to maintain. "Invisible" hand?
The solution is quite simple really: there is no simple solution. If you're going to displace a business you can't replace them with something less then what they were and expect to make more money than they did, at least not in a sustainable way. It's simple thermal dynamics.
This is all a subset of issues born of cargo-cult thinking, techy buzz words and such that give businesses respect they simply co-opted by using the word/technology in marketing materials. More bubbles, more start up trends, more 'combinators separating uninformed people and their money without providing real value and expecting to get their @#$% &*!! for doing us the favor.