Not just SFO and LAX either, you have OAK, SJC and SFO up here, and ONT, BUR, LAX, LGB, and SNA down south. There are flights between any of those combinations many many times per day, and the locations involved are often much more convenient than the HSR depots will be.

The HSR depots are going to be downtown San Francisco, which is a lot more convenient than the pain in the arse SFO is, and LA Union Station, which is rapidly becoming a hub for rail lines going to Orange County, Santa Monica, Pomona, the South Bay, East LA, etc. LA Union station is rapidly becoming a rather good transit hub.