Paradox in U.S. Healthcare?

Normally if buyers preferred to shop for the lowest price goods, then that would incentivize sellers to offer lower prices than the competition, and there would be a race to the bottom in prices.

Given insurance companies are the largest payers and funders to medical providers, and given they prefer to contract with the lower-priced medical providers, then wouldn't that similarly incentivize providers to offer lower prices than the competition, and there be a race to the bottom in prices?

So why aren't healthcare costs going down?