Because until this year, there hasn't been a high demand for passenger trains, or public transit in general - I think the last time mass transit was heavily used was prior to WW II. In the US the goal was a house in the suburbs and a car in the driveway, and many people achieved that. No middle class demand for mass transit - no more mass transit.

Young people are absolutely galled when I tell them that my parents used to put me on a bus to go visit my grandparents when I was in elementary school (back in the '60's). The bus driver had me and my brother sit right behind him, and wouldn't let us off until my grandfather came to get us. It was still fairly common for folks to ride buses, back in the day. (and now I'm going to slink off and look for more grey hairs...)