Prices. If I charged $5 for something the insurance would pay me $50 for then they would pay me $5. If I charge $100 for what the insurance would pay me $50 for then I will get $50. I could charge 1 million for every thing I do and I won’t get paid any more. Insurance sets the prices.
I’m not driving up the costs of healthcare because I’m a small private practice. If I was a hospital employed physician I’d get paid less and the hospital could/would get paid more by the insurance.