Actually, they don't derive the same benefits. They have no cars or counter on-site.

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.