While the other things you list are technically not immediate life-or-death decisions, they still are not voluntary purchases. The presence of any kind of coercion distorts a free market.
Also, I don't want to live in a society where individuals must decide between vaccinating their newborn children or paying their electricity bill that month. Or between getting a flu shot and buying groceries for the week. The externalities of these "individual" decisions are obvious, and a free market has no answer.
Finally, let's imagine a system where emergency care is covered by a national single payer, but "humdrum things" are available in a free market. Now the poor can't afford basic physicals and flu shots, so we all end up paying more into the single payer system to cover such people being hospitalized for conditions that could have been prevented by regular medical checkups.
The number of instances where this dire case occurs is minimal compared to every other instance. Sure, when its life and death its not practical. Perhaps those sorts of situations is where single payer or insurance makes sense.
For humdrum things like physicals, wellness visits, cold and flu checks, vaccinations, routine labs and imaging, etc. a free market could work very well.