But the major reason that rail travel will fail is that rails are a form of public transportation. Americans despise public transportation (I've read something like nearly 4 in 5 Americans have never ridden public transportation once in their lives), mostly on the grounds that it brings them too close to other members of the public.
I think a lot of it is cultural, but availability has to play a part too. A lot of people live in areas where there is essentially no way to travel other than by car. I can barely name any of the bus stops in the town I spent all my high school years, and that has <30,000 people in it. Unless you're either a) in College or b) In the cities chances are carpooling is the closest you're going to get to 'public transportation.'