https://en.wikipedia.org/wiki/Amtrak#Pre-Amtrak
https://en.wikipedia.org/wiki/History_of_rail_transport_in_t...
Basically, an ongoing waterfall of corruption, regulation, NIMBYism, unfair (arguably) competition from other sectors, and a lot else.
It's not quite accurate to just say "Well, passenger rail is dead" as though it was some natural progression of things--especially when you look at it working in other nations.
That said, I'm in favor of keeping amtrak for strategic reasons (a trained pool of operating talent for national emergencies).
A lot of the removal of rail capacity has been short-sighted, and often for the gain of automobile manufacturers.
