In the US, outside of a few special cases, if you're operating on the national rail network, you're operating on rail owned by a freight company, and they have priority. Amtrak often struggles to operate more than 1 or 2 trains an hour as "guests" on these routes. This is very UNLIKE Japan where the freights run on almost a totally different set of tracks.

Also, from a regulatory standpoint, freight and intercity railways (e.g. not subway/light rail/metro/trams) are subject to full FRA regulations, compliance with which would add even more costs, for little real benefit at the speeds they travel at.

Plus, in practice subway/light rail is electrified, and anything else (again with few caveats) is not. In towns with both it is very rare for them to use the same stations.