Could you provide references to that? I took a look and the information I found said California approved it but the governor kept vetoing it. I'm not sure where you got that information from.
I once did a bunch of research into the topic and had the sources saved on a computer, but at some point I deleted them, and I can't find them again. Here is a different source explaining in brief that Vermont, California, and Colorado rejected single-payer and the costs that caused them to do so:
In any case, it's just simple math. Bernie Sanders' proposed plan would cost America $32 trillion over 10 years, or 3.2 trillion dollars per year. In 2018, there were 127.59 million households in America. A cost of $3.2 trillion spread over 127.59 million households is $25,000 per year. If you go by each person instead of each household, it's just shy of $10,000 a year (using a population of 330 million).
The current studies disagree. Even the studies done by right wing think tanks I have seen say that america could cover everyone and pay less. Here is a link to an article discussing a recent study which found america would save $886 billion over 10 years. Every study I have seen says Americans would save money.
The studies you looked at disagree. That does not mean that all, most, or even a majority disagree. Here is a study from RAND examining the effects of a proposed single-payer plan in New York:
To quote their conclusion in full:
"This analysis shows that a single-payer approach in New York could expand coverage while reducing total health spending, assuming that the state is able to negotiate slower growth of provider payments and trim administrative expenses. While these assumptions are reasonable, they are also highly uncertain and depend on providers’ bargaining power, the state’s ability to administer the plan efficiently, and the federal government’s willingness to grant waivers to the state. The analysis also assumes one possible progressive tax rate schedule to finance NYH. This tax schedule would reduce average health care payments for a majority of the population; however, the viability of this tax schedule assumes that few high-income residents find ways to avoid taxation. If only a small percentage of the highest-income residents found ways to avoid taxes, the schedule would need to be reworked, potentially increasing the burden on middle- and lower-income residents. Overall, these results suggest that the single-payer option has the potential to lower payments for the majority of New Yorkers, but the results depend on assumptions about uncertain factors." (italics mine)
To quote the headline of a National Review article discussing the study, "If you assume single-payer saves money, it does." Whenever a study says that single-payer will save money, you need to examine the assumptions of the study. For instance, the RAND study assumed that provider payments will increase at the same rate as in Medicare and Medicaid, which is less than the rate at which private payments are growing. With that assumption, NY's plan would save 3% of their total healthcare spending after ten years. But if you assume that the payments will increase at the private rate, spending will go up by 12% in ten years.
Another study by Charles Blahous of the Mercator institute was used by some to claim that Sanders' plan would save $2 trillion over ten years. However, that analysis assumed that Medicare-for-all would pay hospitals at the Medicare rate. The problem with that is that the Medicare rate only pays hospitals for 87% of their costs. The only reason hospitals can afford that is because private insurers pay 144% of the costs. If that assumption became reality, hospitals would go bankrupt. In order to prevent that, the plan would have to either pay 100% or more, eliminating the $2 trillion dollars in savings, or hospitals would have to make drastic cuts, reducing both the quality of and access to healthcare.