How on earth is this type of pricing legal?
And so this practice thrives.
What's coinsurance? ACA regulates copays, deductibles, and so forth. Ah, but no one said anything about coinsurance. It's totally not a copay, premium, or deductible. See? It's different.
Surprise billing is how hospitals pushed back against insurers. Consolidate and then outsource all actual work, so the hospitals no longer get stuck with the bill. Oh, that specialist you saw in our hospital? Ya, she has nothing to do with us. Ya, you should have asked your insurer if her office has an arrangement (collusion).
This mechanism may be a foundation of legality of health industry pricing practices, but it is grossly abused. Contrary to what is advertised, U.S. health care is not a free market. The pricing is made opaque by insurance industry and other middle man. This is the main reason why price gauging of that magnitude is possible. It is a cash cow that just keeps on giving and trying to change that will be extremely difficult.