You're ignoring how non-dense everything actually is in those places. Americans no longer live in walkable cities and towns like in the early 20th century before cars became popular. After WWII, with the rise of the automobile, the inner cities emptied out and everyone who could afford to moved out to the suburbs. So now, even in a "city" in America (unless it's Manhattan), you absolutely need a car to get anywhere, because nothing is walkable.

It's not like 1905 when you could just walk from your home in Smalltown USA to the local train station, buy a ticket, and get a ride to the nearest city, and get out and walk from that station to interesting places.

Any train trip, even if you look only at the eastern states, is likely to require a car ride on one or both ends to get to/from your source/destination to/from the station. If you have to drive an hour just to get to a train station, and another hour to get from the destination station to your final station, it's probably faster and easier and much cheaper to just drive the whole way. Don't forget dealing with parking, car rental, etc.; you'd probably have to take taxis, and those are quite expensive.

The fundamental problem here is density. America doesn't have it any more.