NavigatorII is correct that firms from UHG, Cigna, Priority Health and others run most (if not all) of the Medicare Advantage Plans because they have the low cost infrastructure to manage those plans.
All three are current of former clients of mine and happen, in my experience, to run very ethical organizations. I cannot speak, obviously, to every clinical admission decision, but for the most part, they perform stakeholder capitalism and try to balance client experience, efficient claims processing, population health and ESG (environment, equity, etc.).