In my world there is a billionaire. She's one of the richest people in the world, comparable to to the very richest people in our real world.
In the country she lives in, there is no significant universal health care. All health care providers are private businesses and receive payment either from an insurance company or out of the patient's own pocket. There is no government law forcing anyone to have health insurance. Emergency rooms have to (by law) treat you for severe emergencies even if you can't pay, but they will try to get you you to pay it back later.
My billionaire is so wealthy that even if she were to get a horrible disease that required extraordinarily extensive and expensive treatment, she would hardly notice the dent in her personal fortune. See is rich both in terms of assets and in liquid cash, as well as precious metals, stocks, etc. She has spread her assets out in a variety of ways, to reduce the risk that a streak of misfortune could remove her wealth.
Expect for the particular details given here, assume the world is similar to the real world, and the country is similar to the United States.
Insurance companies make money by taking on risks people themselves can't take, and they charge for it.
My billionaire pays regularly for health insurance. Why does she do that?
Please note that this is not about life insurance, only health insurance.