It's there to give you an incentive to choose a given airline. It doesn't mean that you are being taken advantage of, per se, but it probably affects the choice of airline.
Let me put it this way, you might get a 25% cashback on a 1000 flight, but there might be a 500 flight alternative from another lowcost competing airline which you didn't even consider or knew it existed due to their points moat or whatever