Why can Iceland setup and maintain a single-payer system but Vermont can't?
From what Wikipedia tells me on the Vermont case, the Vermont government feared increases in costs and taxes from such a reform. In the end, it boils down to what people/voters/decision-makers are willing to pay for a health care system they believe to be good for the people. Scandinavian countries provide lots of top-class public services (health care, child care, education) but also collect the highest tax rates in the world. Apparently, political will and public opinion in Iceland were willing to accept the price attached, which was not the case in Vermont. Beyond, it is possible that the move from the previous system was less drastic in Iceland, requiring fewer things to change.