I'm reasonably sure my home town in western PA lost passenger service on all three railroads before WWII.
As you found out, it was actually the 1950s where the last service disappeared. Same is true in most of upstate NY -- there was a comprehensive passenger rail network still going until the mid-50s, although it was being run with more and more dilapidated equipment.
What happened in the 50s which killed the passenger rail system? Probably the Interstate Highways.
Anderson is correct on why most Americans don't ride trains, but he did leave out reason #1:
- Existence. If the train doesn't go that way, you can't ride it. For instance, just try to get to Detroit from the east.
I believe the second-most-important reason, #2, is:
- Reliability: people will tolerate a lot if the train operates exactly to schedule. If a route which had poor schedule adherence achieves goods schedule adherence for a year or so, this is documented to raise ridership by a lot -- and vice versa if schedule adherence drops.
Reasons #3 and #4 are speed and frequency, and I'd put them at comparable importance: you need some of each.