A good question. Why doesn't it? Could it have something to do with vested interests? I don't know. But it does seem to me that if the USA had high speed rail between, say, the major cities on its Eastern seaboard, and there are an awful lot of cities in there, vehicular travel and air travel between these cities would drop off. The answer, less money for the companies who now cover these routes.
Might sound a bit silly. But no more than silly than the reason Los Angeles didn't take to rail because the big oil companies were worried they'd lose out on the huge profits they made on petrol sales if rail networks went in.