CAHSR was opined years before SR 85 and 87 and before VTA light rail.
It's the perpetually never-happening, chicken-vs-egg aspirational project for mass transit in an area dominated by urban sprawl and car-first infrastructure that would need massive investment in local mass transit like Japan first.
LA has been investing very heavily in mass transit for decades, fwiw. If the terminals (SF and LA) can be navigated by transit, then leaving the car at home and taking the train becomes a plausible option for most people.
It always made more sense for me to leave the car at home and take the train to Chicago than deal with the traffic and parking in the city, it's hard to imagine SF being that different in that regard but i haven't been.
20 years ago, parking in SF was hell. I remember driving around and around for like 45 minutes to find a spot and the fun of parking on a hill with a racing clutch in a spot only a valet could fit into.
It's the perpetually never-happening, chicken-vs-egg aspirational project for mass transit in an area dominated by urban sprawl and car-first infrastructure that would need massive investment in local mass transit like Japan first.