Just when you thought "health care" in the US couldn't get any suckier...concierge medicine.

[upaloopa]

2. I was a controller at a medical clinic.

we had 21 doctors on payroll and more on contract. They were paid a percentage of the revenue they generated. We were reimbursed by insurance cos. and Medicare and MediCal ( CA calls Medicaid MediCal)
Many if the doctors had an income level and work load they were comfortable with. It meant being well paid and working less than 40 hours a week. Not all doctors were that way. Some were very dedicated to their patients and worked long hours which had the effect of them not enjoying an easy life style.
I did a study and found out that for us to make money at the clinic the doctors had to see more patients and spend less time per patient. And nursing staff who worked solely for a doctor could only work when the doctor was there.
I think these are the reasons for the type of medicine described in the OP. Doctors who have a lifestyle they are comfortable with work as much as it takes to achieve that life style. The more the patients pay them the less patients they have to see.
I think with the ACA doctors taking the insurance would have to work more hours than some of them would like.
Medical care requires trained people to provide the care. It isn't something like going to the store and the more shoppers there are the more product we make.
Medical care is a limited resource. Limited by the amount of medical staff are available at any one time.