Why? Because the roads and automobile industry are what get the subsidies and support, and because Amtrak's been pretty poorly managed for a long time. Around here an issue is that the tracks are owned by freight train companies so that passenger trains have to wait. It's common for trains to be delayed for hours.
Our line from here to Chicago is pretty nice, though, for the same reasons the NE stuff is - there's the volume.
I'd like to see government support for mass transportation but that's not where the rich & powerful guys are.