I'm not sure we can't do that. I believe I read something about cuts in non-essential operations for the elderly in Germany's public healthcare system, but I can't find it any more because Google sucks. Still, I don't believe that's taboo if the other option is to have the system crash.
Why not? It happens a lot in 'Europe'. (yes I know that 'Europe' isn't one single thing)
The fact is, and remains, that the 'right' thing to do is to ensure adequate service provision and that the 50 or 60 or 70 or 80 year old who needs a hip replacement, or aortic valve replacement, or high level care nursing home, actually receives it. But the powers that be, even now, are able to reduce the current impact to healthcare budgets (and thus government expenditure) by pushing waiting lists out to such an extent that people are rendered basically invalid by the wait times, and die on them.
It's not just europe, it's basically the rule in the US (unless you are independently wealthy or have a decent healthcare plan), and it will only get worse unless people unzip their trousers and make the beast that has two backs.
Or, we decide collectively that the attempt at death by a thousand cuts is not in any way acceptable. Which is hard because the insidious nature of death by a thousand cuts is (to absolutely mix metaphors) that you don't notice the temperature rising until you are parboiled.
So no, just because it's technically possible to replace an 80 year old's hip, doesn't mean we should. There is nothing wrong with some cutoff where we say 'as a society, the maximum we want to pay for a daly is x' (or qaly or any other measure you want to take). There is nothing wrong with being honest about resources being finite, and that not every potentially possible medical intervention needs to be paid for by society. And this is what is happening in 'Europe' (although it isn't admitted as bluntly as I put it here...), and what I was referring to.