It's cheaper because less is offered. Of course one can argue the extra you get under the US system doesn't really add value.
Keep in mind that single payer systems are struggling with costs as well. It's just easier for them to say "no one gets this new treatment".
And yes, you can very easily argue that many other costs don't add value. That's why pointing to the superior overall life-expectancy in other countries is such an important part of the argument. On balance, every other system in the developed world does more, for more, with less. Our system offers bottom-of-the-pile rankings by every major measure.
Finally, "struggling with costs" is a non-starter as far as arguments against single-payer go since what things cost and how you come up with the money are clearly two different things. Saying "country X is having a hard time funding their health care system at 10% of GDP" in no way undermines the case for dumping a system here in the US that costs us closer to 18% of ours.
Seriously, we could make massive improvements to ours simply by picking the name of any other OECD country from a hat, and just implementing their system. Literally anything is better than what we've got here, and it's not even close.
There are plenty of drugs you can get in the US that single payers systems simply won't cover. The Cancer Fund in the UK is a great example. NHS said "nope too expensive" to several drugs so unless the Cancer Fund pays for it, you're SOL. That's how single payer systems save money.
That's why pointing to the superior overall life-expectancy in other countries is part of the argument.
Life expectancy is a very blunt tool when you're looking at level of healthcare. There is too much intra-country variability.
The point of controlling costs is to provide incentives for developing drugs that not only work, but that do so at non-ruinous prices.
And also, the cost of those HCV therapies is actually cheaper in the US than in the EU.[1]
[1]https://www.forbes.com/sites/johnlamattina/2015/12/04/for-he...
The thing to recognize is that the every-person-for-themselves approach leads to outcomes that drive costs up extraordinarily. Avoiding the US model is why every other OECD country offers universal coverage and boasts longer lifespans, even though health care costs them one half to two thirds less a portion of their GDP.
For all its bleeding-heart, hippy commie values, the major advantage of single-payer is massively reducing the costs of health care, and making life very hard for anyone not directly creating value. This is bad news for rent-seeking holders of pharma patents and CEOs of private insurance companies making $20 million per year, good news for just about everyone else.
It comes down to this: will you accept that some forms of socialism work in return for getting a better deal on health care and the indirect benefits of living in a society where access is a given? Or are you so ideologically committed to free-market fundamentalism that you would rather waste more of your own money and live in a more unstable society because hey, that's how John Wayne did it.