Even if you could solve the impossible land acquisition problem and build non-stop highspeed rail in a straight line between LA and NYC, it'd still be much faster to fly the ~2500 miles than to take a train. It's 6 hour flight vs a well over 12 hour train ride.

Passenger rail doesn't exist on that scale in the US because it's prohibitively expensive and, even if it were free, obsolete at that distance. It could be better for intrastate or travel on along the coast, but then you run into the land and cost issues. See: California working on this for nearly a decade.