they don't, for the simple reason that if they did all you'd need to do is go to the hospital and pay out of pocket, most US states don't require you to have health insurance. (or switch your insurance provider, as you pointed out there are many).

There's no logic in what you're trying to argue. Healthcare providers charge for their service, insurance companies negotiate that cost down, next to risk management that collective bargain power is the reason you buy insurance in the first place. Again if what you're saying is true all you'd need to do is just buy your healthcare from the hospital directly, if you end up in the ER take a look at the bill and tell me how that went