They build roads going every direction because people and stuff needs to go every direction, people still need to go to those places if you replace them with trains.

Also the effort to fix and replace train lines is far more than fixing roads, I think a lot of Americans haven't really used trains much so they don't comprehend how complex it is, when you've had trains cancelled for a thousand dumb reasons like the wrong kind of leaves on the track then trains don't feel as reliable - and when the track is blocked for repair they can't go round so it's bus replacement service so if you scrap roads then you need redundancy so you end up with masses of tracks everywhere.

I love trains but people need to learn how they actually work and the costs involved so we can be reasonable in planning and build the most useful solution for each situation - just saying trains for everything doesn't make sense.