It’s all about population density and distance.
To put it in perspective, Tokyo-Osaka (which is profitable), services 3x the number of people over half the distance.
Even the Boston - Washington corridor is only 50 percent as efficient as Tokyo-Osaka and that assumes ridership numbers equal to Japan.
Those are cities that are what - two hours apart? And with the bullet train in Japan that distance can be traveled in 45 minutes. With the distances in California and almost no body lives in the mountainous corridor between Los Angeles and San Francisco, it means that the ridership to support it isn’t there. And with competition from the airlines, it will be operating at a loss from Day One. Which means ultimately the taxpayers would have to pick up the tab for this White Elephant.
Better to kill it now while its still a snaggle-toothed baby instead of a full-grown monster.