The US HC system basically runs as a "skim" operation. Since skim is fundamentally percentage based, the more money that flows through the system, the greater the absolute amount that is skimmed. Thus, no one has incentive, in the long run, to reduce costs. Short term, insurance companies might benefit from cutting costs, but they know that ultimately, when costs go up, they can justify proportional premium increases, which increase their skim in absolute value.