(Insurance companies have legally limited profit margins on health insurance.)

Does multiple private insurances add a little administrative overhead? Sure, but nowhere near as much as you see in the OECD figures.

There are many reasons why US healthcare is so expensive.

Some of them have to do with litigation: Skyhigh insurance premiums and a medical “Cover your ass”-culture with unneeded tests and MRIs done on a regular basis.

(In Canada, there is a legal ceiling on how much in damages you can sue a doctor/hospital for. This would be a good idea to implement in the US.)

Another added expense is free riders: All the people that show up in the ER, whether because of the flu or a gunshot, get treated/operated on, and never pay their bill.

Another issue is that the US has some of the best doctors in the world, and new, prohibitively expensive treatments are often introduced here first.

Many, very expensive treatments simply aren’t done (or done very rarely) in countries where the public (fully or in part) pay for treatments.

Waiting lists are another way of limiting costs in European countries. (Waiting lists that can be over a year long, but their healthcare systems are arguably cheaper to run.)

I could bring up some new medicines that in the US cost thousands of dollars per week (Crohns medication for example.) In European countries those medications simply aren’t available, or are only available on an exemption: Meaning that your doctor need to apply to have the cost covered, and is usually turned down.

Another example would be something like SRS surgeries.

These can be extremely expensive, and are covered by insurance, which of course increases the costs of coverage for everyone.

In European countries you’d either face a very long waiting list to get the operation covered, or you wouldn’t be eligible for it. Or only eligible after jumping through extensive hoops.