One BIG problem in the US is the huge distance between cities and other points of interest. There's a relatively small handful of corridors in the US that have Europe-like distances between cities. One of them, obviously, is the Northeast Corridtor between D.C. and Boston. Another is the Chicago-Milwaukee corridor. You could probably also do something in the L.A./San Diego/Inland Empire triangle. But for most of the U.S., even high-speed rail would turn intercity train travel into a multi-day affair, whereas a jet airliner can get you between the most distant city pairs in the lower 48 in a matter of hours. When you have US-style distances to cover, trains are a lose.