What stops an HMO from letting their patients die from expensive but treatable illnesses?
As a for-profit corporation, (or a nonprofit HMO that has lavish salaries for their management) they have every financial incentive to do this. Sure, patients could sue, or state regulators could investigate, but the HMO can throw up a smokescreen of documentation, or it can just be extremely slow to approve expensive treatments, hoping the patient will die in the interim. Any lawsuit is going to come up against top tier attorneys, and the HMO’s medical directors who will swear under oath that nothing more could be done for this patient.