Try looking at somewhere that does have high-speed rail, rather than only considering Amtrak's broken offering.

As an example; consider the journey from Paris to Nice. It's a 580 mile drive taking ~9 hours, a 1.5 hour flight costing £129 or a 5.5 hour train ride costing £71.

Once you include the hassle and time required for airport security, the gap between the train and plane closes significantly. 1.5 hours flying plus 2 hours at the airport before takeoff and another half hour after landing takes it up to 4 hours already, rather than the train where you can just walk into the station and get on. Then there's the comfort and facilities on-board. A cramped economy flight Vs a comfortable train with leg room, space to move around, charging plugs, etc.

When you look at it like this, is it worth spending nearly twice as much for a slightly faster but less comfortable journey? High speed trains excel over middle-distance journeys, too long to comfortably drive but too short for flying to really make sense. Imagine a train that would take you from the San Diego to the centre of San Fransisco in less than 5 hours, running 10+ times per day and costing less than flying. That's the reality of high speed rail in many countries. Can you really not see a market for it in the USA?