This is the basis of all Medicare Advantage Plans, where the physician or their employer gets X$ a month per MAP patient and must pay for most of the cost of care. The insurance company gets to keep most of its share of what Medicare pays. Nice profit ensues for the insurance company.
Insurance companies that sell Medicare Advantage plans end up keeping only a tiny fraction of what they're paid, hardly "most". This is a low-margin, high-volume business. You can find the details in their published financial reports.
