Because there's no incentive to stop extorting the uninsured. That's all this is.

Medicaid and Medicare pay fixed fees set by the government.

Insurance companies negotiate "reasonable" fees for services.

As I have insurance, my medical bill usually looks something like...

Procedure A...... Amt Billed: $2000.......Paid by insurer: $100.... Amt Owed: $25

Where $25 is my co-pay and $100 is the fee the insurance company negotiated as "reasonable". For in-network care, the contracts disallow "balance billing" (trying to collect the $1900 in make-believe charges). For out-of-network (no negotiated rates), the hospital often will balance bill (except where prohibited by law).

It's a completely ridiculous system in which "non-profit" hospitals make billions (and write off those imaginary "losses") and insurance companies (who have to pay our ~80% of revenue on care) are happy to have inflated numbers all over the place because 20% of 100 billion is more than 20% of 10 billion.

There is no economic advantage of offering lower prices in the US medical sphere, as there is no way for a patient to know that you charge less than another provider. Most medical practices do not provide any form of costs until after a procedure except ones usually not covered by insurances, such as dental and chiro, which do offer transparent and low prices because they compete in the free market.