Or, it being too confusing. That's a problem with health insurance, and not with money.
That's why some think that a national health care system that is designed primarily around effectiveness of distribution of payment, rather than extracting maximum profit from the flow of money between patient and provider, is the moral and effective solution.
To your last point, rationing low availability health care is nothing new. Alcoholics can't get liver transplants for example. There's a whole field of bioethics that can surely answer some of those questions.