It's a relatively simple mix of economics and politics. If the only thing we changed was a single payer, without changing anything else, prices would continue

It's a relatively simple mix of economics and politics. If the only thing we changed was a single payer, without changing anything else, prices would continue skyrocketing and the government would either have huge deficits or very high taxes, even compared to most of Europe: US healthcare is that expensive. To make single payer work, what the US would have to do is to also force prices down. This can be done through price controls, like in Singapore, by directly owning hospitals and employing doctors, like a good percentage of Europe, or by increasing the supply of healthcare providers so much that prices must go down. Any and all of those things would cause an upheaval in the healthcare industry: A lot of jobs would be lost, and others would pay a lot less. Many investments, like those of hospitals that compete with each other by being the most luxurious and with the most MRI machines, or pharma companies that expected to be able to charge a whole lot more to US patients than they do in Europe, would go down the drain. Every single bit of extra US healthcare expense an inefficiency is benefitting someone else. More efficiency when driven directly by government mandates, like a single payer system would aim to do, is a wonderful way to lose elections. This is not just why democrats don't really pursue single payer seriously, but why republicans don't propose any changes that would really make the system more market driven: It's hard to rein the profits of an industry that is over 17% of GDP.