Don't you understand?
It's the transport for the post-carbon future, when autos & planes will either be too expensive to operate or just outright banned. Did you not see the picture above? The new trail will be propelled by windmills, solar panels, and self-esteem.
But seriously, you are correct. They've been talking about this for 40 years. As a former resident of California, I once even thought it was a good idea. The problem is that they can't make a viable business case for it. The ridership numbers they provide are simply absurd. Their cost estimates are fantasy. If the business case was as wonderful as they say, it wouldn't need taxpayer funding at all.
And you missed one: HSR "works" in Europe because it's totally subsidized. I love traveling by rail in Europe. But every time I do, it's with the knowledge that my 1st-class trip is being paid for mostly by average citizens with a much lower standard of living than I have.