Free market, because first, rail leads itself to monopolies. Rail infrastructure is expensive, and you need significant area coverage until you can get enough customers. So if you built one, you as a rail provider will go at extracting the most possible value, since you don‘t have competition. Classic free market failure. The solution here would be to have at least four (proven number to avoid oligopolies) private train providers competing on public infrastructure. Since Americans shudder already at the word „public“, that‘s a significant hurdle.
Individualism because in the US, people have a propensity to not share rides with others. Same fear of „public“ IMHO, as long as public transportation is thought of existing solely for poor people until they can afford a car, nothing is going to change.