I guess this is where my geographic bias showing, since I am surrounded by small hospitals with a poor payor mix and it's standard for hospitals to offer EM group subsidies. Even the CMGs get subsidies from these hospitals.
Operations, staffing, etc. are necessary but generally static. You know the costs of your business should be relatively fixed. Staff the ER, pay for billing/coding services, etc. ED volume tends to be fairly predictable (outside of acts of God, like COVID) and the payor mix tends to run static for a given location (I.e. you don't just suddenly have a few months where you get all uninsured patients). So you run your business pro-forma with all this in place and you figure out what kind of subsidy you need from the hospital to get to a staffing cost that gets you warm bodies in the door, assuming the volume/payor mix itself cannot support minimal staffing. The subsidy may be a small piece of the pie but it's the least static portion of it.