You're ignoring the time element of healthcare. If you get hit by a bus, you aren't in a position to shop around or negotiate for care. You can even be incapacitated and unable to respond to questions before your treatment starts.

Imagine you get knocked out cold and wake up seated at a restaurant with an empty plate of food. You were fed the food but you have no memory of it. The bill comes and it's $5,999. Would you feel like this is fair?