Well that's the point, I think everybody should be taken into account in order to paint a comprehensive picture of the quality of the system at country level. The resulting stats reflect the health of a society as a whole not just of the part that can afford it. Not having universal healthcare is still part of the system, even if we don't like it.
I get it that health outcomes of those left out are probably very different. But leaving those numbers out of the comparison doesn't really work with these type of statistics.
At that point how could you compare it to the other countries that take everyone into consideration? The stats are GDP/capita percentages, should I remove the ones who can't afford healthcare from the GDP stats as well to not skew the ratio? I don't really like where I might end up taking this route.
I don't have any experience with US healthcare and I'm sure the quality of the services is really high, but the fact that you need to afford basic healthcare and it's not guaranteed by the government for everyone makes me see it as closer to just another "consumer product" compared to other systems.