> It's hard to imagine a treatment cost so high that it wouldn't be worth the USG paying for it.

Given that this is also true of universal health insurance and the US government also doesn't pay for that...

They (we) do, just for groups that incur the highest medical expenses on average. Why we can't just open up Medicare to all is beyond me, adding on the portions of the population who are on average the healthiest (and who are already paying for the people on it) would not push up the cost significantly.