When I hear single-payer healthcare, I don't think about the Canadian system, but the English system, which is terrible, compared to the quality of care you get in Germany, or most people get in the US.
Which brings me to another reality: Most people in the US have access to a very good healthcare standard. It's not so much that they don't want all people to have that, but they do wonder if that requires a complete change of system for them.
So, I don't know much about the English system, but I do know the NHS is very popular in England. Are you sure it's actually terrible? Or could there be an element of the same propaganda I see in the US about the Canadian system, like people waiting months to see a doctor, etc.?
Which brings me to another reality: Most people in the US have access to a very good healthcare standard. It's not so much that they don't want all people to have that, but they do wonder if that requires a complete change of system for them.