One reason for this is that many of those patients who need very serious treatment die before getting it...seriously. Check out the wait times and death rates while waiting for treatment, and you'll see how high they are...and realize that these are great systems, as long as you aren't too sick.
Talking point(s) I haven't heard much...
Increasing healthcare costs?
If a person wants 1970s care, it's available at a low cost. But today's care costs a lot more, because someone had to develop new techniques and equipment. People often insist on the latest care. If we go to socialized medicine, there's little incentive to get improved methods. "Do you want new advances in health care, or do you want universal stagnant care?"
Many people come to the US for care they can't receive back home. Once the US goes socialist, (a) where will we go for quality care, and (b) where will the rest of the world turn when we aren't there?
The problem is that the data on US life expectancy rates is not nearly as good as it is in other industrial countries. Apparently, an even more important statistic for measuring the quality of health care is infant mortality rates and in this area the US system performs poorly compared to other countries.