One big element is that a lot of large companies and non-profits run their insurance programs as self-insured. They pay the direct costs of the medical care of their insureds, and keep the annual premiums the entire employee-base pays. The "insurance companies" are paid a percentage of the total revenue/claims as an administration fee, so they have incentives to push the overall amounts paid up, not down. Self-insuring eliminates the profit overhead of the insurance companies, but screws the incentives.