That's because American rail transport is fundamentally broken, not because rail in general is broken

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?

There is no market because passenger rail is inefficient.

Because rail has no market, there's no incentive to make passenger rail more efficient.

The circle of American transport since the 60s.