It's fairly common for governments to provide a basic level of care for free or heavily subsidized, but not cover more expensive treatments. It's certainly not exclusive to the US.
But it's not like there is some kind of upper limit on coverage. If you have cancer, you will get treatment regardless of how much your care has already cost.
Every single one of those criteria is subjective, which is why you see these fundraising campaigns for kids with cancer to go and a get a multimillion dollar treatment in the US, because as a parent, accepting that there’s more you COULD do if you just don’t give up is hard.