We have more people stretched out over more land with more varying regions with more varying needs and costs with more conservative social, political and economic values. Nearly all of our trade involves trucking and cargo ships, with freight making up the raw material shipping that isn't time sensitive.
It makes no financial sense whatsoever to fund railroads. We have extensive interstate highways and most of our people have cars. Why pay for a railroad the size of Europe when you don't have to go all over Europe, and all your needs are met via the existing shipping mechanisms? What would be the point?
If you took our cars away, maybe it would make sense, maybe. But before we pay for railroads we might need to pay for our health care or education.