This is a point I don't see raised nearly often enough. If their profit potential is capped at a percentage of total revenue, they have absolutely no incentive

This is a point I don't see raised nearly often enough. If their profit potential is capped at a percentage of total revenue, they have absolutely no incentive to truly attempt to reign in costs. As out of control costs can be used as evidence that, through no fault of their own, they need to increase rates substantially year after year.