I agree with your point, and there is likely a business case, society wide, to average health care costs across the population. People are less productive when they have major, long-term worries, and even folks who are young and healthy today think about the possibility of being very sick.

And in a society where sickness implies economic misery, people plan by building their own, ad-hoc mini-safety nets which are often less valuable and more expensive than a standardized solution. So most people would support averaging health costs if they perceive it as mostly efficient. That is, they would not mind a sick person next door getting treatment while paying the same cost as themselves. But if they think a bunch of doctors and crooks milking the system by making up and billing for fake services they will strongly push back. My 2c.