Typical the argument is that a single payer system is to avoid waste. California Government would be the perfect candidate for this since they are so fiscally responsible and do such an amazing job managing their finances. God Speed.
California has benefited from the Federal spending bonanza and also has famously high tax rates, treats capital gains as ordinary income, and has a lot of rich people. The FTB seems to have screwed up the links[1] and I can't find later data for a complete fiscal year, but check out "Ordinary Dividends" and "Capital Gain" in exhibit A9 for FY2019[2] to get a sense of how important that is to the state budget.
[1]: https://data.ftb.ca.gov/stories/s/Other-Tax-Data/sgxz-494k#d... [2]: https://data.ftb.ca.gov/download/d6s8-gyup/application%2Fpdf
I love this state’s geography and food scene, but the various governments here (local, county, state) aren’t exactly the pinnacle of smart governance.