I haven't gone deep into the economics, but I've found rail cost several times as much for a 30 hour ride with nowhere to sleep, compared to the 2 hour flight or 20 hour drive. So of course ridership is low.

Some intersection of actually-competitive pricing and higher speed tracks, and it seems like rail would have the potential to be plenty competitive. Lower vehicle purchae, maintenance & fuel costs, greater comfort. If I could make a 2 hour flight in 4 or 6 hours by train for 90% of the cost, I'd probably never fly again.