* older: the railroad was invented in the 19th century, and I think the US railroad network circa 1900 was superior to Europe...
* smaller: not really... depends where you count.
* more population dense: nobody is expecting good rail transit in Wyoming or Montana (although, Scandinavia seems to do okay with low density). The Northeast, Midwest, and California are all very dense and still have much worse rail transit.
The Northeast really isn't that bad for trains but it does suffer from the fact that there was a multi-decade exodus from many cities by both residents and companies for a variety of reasons. That didn't exactly encourage investment in rail infrastructure.
* smaller: not really... depends where you count.
* more population dense: nobody is expecting good rail transit in Wyoming or Montana (although, Scandinavia seems to do okay with low density). The Northeast, Midwest, and California are all very dense and still have much worse rail transit.