Because it’s not a fair market. Health insurance is a cartel market.

Let’s say you break your ankle - maybe a reasonable cost for resetting the bone would be 240$ - the hospital will set a list price somewhere like 1300$ for the operation and then Anthem/UHC/whatever will send a rep out to be like “Hey, what if, when it’s one of our people, you only charged 300$” suddenly the rep gets a bonus for getting a “good deal” the insured patient is happy to pay well below “market” price and the hospital might get a small kick back for being so generous.

In this scenario most people only ever feel the 300$ price - but uninsured people or people out of network get absolutely fucked.

Since the current system entrenches all the existing players none of the participants (except the patients who usually don’t even get to choose their insurer) want to change anything.