> I suspect that's because of multiple trains per day on the Surfliner.
This is a surprisingly common misconception in the United States. For public transport, the top three determinants of ridership are, in order, frequency, frequency and frequency.
As a simple example, here in the equally long-distance-transport benighted state of Australia, there's a shiny train line that goes from central Sydney to the nation's capital Canberra in a bit over 4 hours, which is quite competitive with driving (~3.5 hours pedal to the metal, realistically 5 with Sydney traffic and breaks etc) and flying (45 min in the air, but several hours of hassle to get to the airport, security, waiting around yadda yadda), and the cost of a return ticket is on the same order as the gas to drive back and forth, and around 3-4x cheaper than flying.
Yet I almost never take the train, opting to drive or fly instead. Why? Because there are three (3) trains a day, leaving at 6 AM (nope), 12 noon (meaning you spend the whole workday on the train) and 6 PM (well, this one's semi-decent, although it's past 10 PM by the time it arrives). And should you miss your train for any reason, you're completely screwed.
If, on the other hand, the trains ran hourly, none of this would be a problem: I could pick a time that suits me, instead of having to fit myself to the trains, and missing one would be an inconvenience, not a catastrophe.