The cost of running rail to supply all the routes currently served by truck now (and generally in the last 50-60 years) is so high that it's infeasible. The less populated and poor the destination, the higher the costs (and most remote areas are both sparsely populated and poor). I think you're seriously underestimating the vastness of the US and the remoteness of the majority of it. Sure, given enough investment and dedication, a nationwide rail network would have been possible but the decision to build America as a car/truck country was taken in the late 40's/early 50's and it's too late to reverse that, even at a governmental level. People expect to live in remote areas now and have all the comforts of a city. That's simply not possible with rail at a sane cost. Not only are cars and trucks more flexible, but the transportation expenses can be shared between commercial and personal transportation. People in America generally don't take trains (and don't like them) and outside of small regional areas, passenger trains are mostly a novelty that run sometimes days late. Between the geography and people's attitudes/expectations, there is no room for trains in America and it shows.