It's hard to know for sure, but the majority of these flights are probably going to be transfers. I've never set foot in LA but I've taken that flight several times.
Even so, there are only ~20k daily seats between the two cities. The ridership on successful high speed rail lines elsewhere in the world are measured in the hundreds of thousands per day.
Why couldn't one part of the journey be by rail, and the other by air? There is a already a lot of shared planning to allow this to happen, with some railway stations even having IATA codes.
I agree this is the ideal situation, but as it stands CAHSR is planned to terminate at union station in LA, quite far from LAX. Ideally LA metro or metrolink would build a direct connection between union station and LAX, but that hasn't begun to be planned and unfortunately it's very difficult to get transit built in LA. For instance the Sepulveda line— one of the most important lines for LA— is at risk of being killed because ticket master's ex-CEO doesn't want a train line running under his house.
That’s ridiculously high demand.
https://simpleflying.com/san-francisco-los-angeles-flight-ma...