But there is only one provider a doctor has to negotiate with in those cases, the US government. It would be much more complicated for doctors to negotiate and set up billing systems with perhaps dozens or even hundredz of insurance companies.
All doctors and hospitals bill by code, insurance pays by code. Most insurances pay prevailing rates by area. A standardized insurance billing form would work and doctors could negotiate charges at prevailing rates or agree to write off charges over prevailing rates.
Rates are lower for instance in Alabama than New York. Also, doctors could as they do now, not accept insurance coverage from companies who do not pay well.
If I were buying insurance in Nevada and doctors offices said we don’t accept Homehealth, I wouldn’t buy Homehealth insurance. By the way, Medicare is terrible about paying.
Disclaimer - in an earlier life I handled billing and insurance for a doctor. Getting any insurance to pay is a mind game for sure.