I was wondering the same thing. I see the difference in my primary care doctor who does not take insurance. So much less overhead, same salary, and better patient outcomes. There is a multiplier effect, as you add people at some point you might need an office manager and then more nurses to keep up quota but for every new dollar of revenue you make the margin goes down.

You wonder how much of a hospital is true emergencies vs scheduled care. While ERs are indeed busy, how many of those should actually go to a primary care doctor instead. Even then I would imagine your schedule appointments are the bulk of the volume at a hospital.