One rationale (well before/without AI) is that medicine operates at 2 levels of hierarchy (doctor, nurse) whereas most fields operate at 3 levels (say exec, mgmt/expert, worker/employee), typically mapped to 2-3, 4-5, and 7+ years degrees in most countries.

It's been argued in many countries that medicine could get cheaper if only 10% of doctors-only gestures and decisions could be delegated to some 4-5 years intermediary medical degree, above nurse and below doctor. In reality it's more like 50% of doctors' work could be offloaded. Which also has the benefit of mechanically addressing the general lack of medical doctors in rich countries with aging populations.