As to the business management point from OP, that is the reason we have a division of labor. Some people in the medical industry will handle the business side, so the doctors can get to doctoring in peace.
“Doesn’t it make the most sense from a societal good stand point to have centralized administration facilities”
The facilities could be centralized, but the administration need not be. For instance, you could think of the hospital like a mall. The mall offers certain services to its tenants, but each store still has to make rent. What actual form of organization of health care services is partially determined by the market and partially by government programs and regulation. What “should” these government policies be a tricky question. I think it is less than clear that your policy would actually maximize societal good.
For instance, when you talk of cost of capital, you likely are thinking of the businesses cost of capital. What about the cost of the doctor’s human capital. Years spent learning their trade before they can make money. For some small, independent clinic the extra profits go to the doctors as effectively compensation for their human capital. We already have a shortage of primary care physicians. If a central authority reduces their compensation further to have the cost of capital be zero, then how many people will become this kind of doctor (oh, but then you say they shouldn’t have become doctors anyway).
Lastly, I don’t understand why healthcare is somehow different from any other business. For instance, in the 1920s and 30s there was a lot of talk that societal good would be maximized by taking over X industry and reducing the cost profits to cover the cost of capital. This strategy has largely failed. There certainly are some cases where it makes more sense, like common pool resources where private property rights don’t work as well. Nevertheless, for most industries, it is better to let the market determine how firms organize themselves. To the extent that the current way doctors organize is conditional on a plethora of government policies, it is by no means clear what the next best step to take is. It makes the solutions very complex.