Why? US health care is proven to be inferior to that of many European countries.

I suspect the reason that AMA limit access to US markets for foreign trained doctors is because limiting the supply of doctors in the US would likely increase the average salary for current US doctors.

Because it sets baseline standards. Yes, I think everyone knows the US does not have the best healthcare in the world. But I also think it's 100% appropriate to say if you want to practice medicine in this country then you must meet our standards. Just like a drivers license might not be valid in any country you visit outside your own.

They don’t just need to re-do the testing; they need to waste six years and another $300k of tuition to learn things they already know, before anyone will be willing to test them.

That's because residency programs are completely messed up.

But this is just one of the many reasons for why medical care is so expensive in the US.

This applies to technology as well: I want the people writing code that will be deployed in $CRITICAL_SITUATION to pass some baseline aptitude test set by US regulation, ideally with some ethics component. Unfortunately, no such thing exists in software and there's a surprising pushback.

It sort of exists. P.E. Software engineering like most of the other engineering branches use. Signing off on designs that require regulatory approval often requires a PE. In my first job in mechanical design etc. it was understood that I would get this as soon as I could.

However my understanding is that almost no one gets this in software and it’s being discontinued.

In what country? I have heard that this is required in Canada, but I've never heard of it in the US.

US. It's so uncommon though (in software engineering specifically) that they're apparently dropping it.