The answer is there’s already a doctor shortage, and the US simply does not have the capacity to effectively 2x the doctor-patient ratio.

Doctors are also unlikely to want a 50% pay cut in exchange for shorter hours. They aren’t directly exposed to the risk caused by fatigue since they will have malpractice insurance. Therefore the safer method of care would be simply too expensive, and doctors wouldn’t see an upside.

Part of the shortage is a result of artificially constrained supply as there aren’t enough med school seats to keep up with demand.