The key point is that they don't want control over them.
They want someone who will be a "black box" so that they don't have to deal with physician recruiting, management, staffing, etc.
It is essentially the same reason why they hire contractors to do the laundry, or security, or food services, or whatever else.
I will use my lawn as an example. I used to enjoy the riding lawnmower but age, arthritis, and prostate cancer mean that is no longer an (enjoyable) option. Now I could hire someone to do fertilizing, weed control, etc., and a kid to mow, and someone to do landscaping, and someone to do the weeding .... or I could pay the one local guy who said he would handle all of that. I pay about $100 a month premium, but it is worth it not to have to deal with 4 or 5 different people and all the conflicts.
That is basically how the CEO/COO/CMO view this stuff. They would rather sacrifice some income so that they don't have to think about staffing.