Sure, in some other countries, for-profit health insurance is illegal.
There are many more for-profit hospitals in the US than there were 40 years ago. Many not-for-profits sold out to for-profit companies. I believe John Oliver or VICE did a piece on this years ago.
Then there are the doctors. Only in the US is being a doctor insanely lucrative. Not all US doctors are out to financially abuse patients, but there are enough who are complicit in the hospital and outpatient practice system who enable mass exploitation.
Single-payer wouldn't end this. Medicare for all wouldn't even be close to fixing the problem. Most of Medicare is administered by for-profit health insurance companies. Medicare pays, but doesn't cover 100%. It still requires paying for one of a laundry list of letters Medicare supplemental and prescription plans. Also, the US doesn't have a functional mental healthcare system. And that's not covered either. Dental and vision also aren't covered.