> California is about the size of Japan with the same GDP.

On the surface, this is true, but it ignores taxation structure when comparing a federal state to a sovereign nation. It would be very hard to get state-level income tax rates above 15% in the US. That cannot compete against federal/national tax rates that normally approach 40% in US and Japan. In any nation, the vast majority of large mass transit project construction costs are paid for by the central/national gov't. I would characterise your comparison is disingenuous.

    > They could pass their own funded project for public transportation.

They could not reasonably 100% self-fund large mass transit projects. They need federal dollars, a lot of them, and it is very competitive to get them. As an example, look at how long it has taken to raise necessary funds to build the Silicon Valley BART extension. There is tremendous support from the public for this project, but it takes a long time to raise necessary local funds. In parallel, they need to "win" federal support for the lion's share of construction costs.