Japan isn't an outlier, there are other countries with universal healthcare that are also high functioning, like Canada (Ranked 7th in public health and 5th in quality of life), Norway, Switzerland, Finland, Denmark, Germany, Sweden.

Not to mention if it was on the median so bad for citizens you'd see more broad support for repealing it in countries where it is supposedly isn't working, but that isn't really happening either.

Switzerland doesn't have universal healthcare. It has heavily regulated private insurance market.

Private insurance is not the reason healthcare is expensive in US. The reason is that services and drugs are too expensive because of collusion, lack of sensible regulation and lack of competition.

Private insurance and universal healthcare aren't mutually exclusive. Even the poorest Swiss get healthcare via subsidised basic plans.

The poorest in the US get free healthcare too (Medicaid). Not even subsidized. Just free.

Status quo bias is powerful