Railroad tracks don’t work like roads. They were almost entirely built and operated privately by companies until the 1970s when passenger rail collapsed and the federal government bought it at deep discount and gradually sold off a great deal of what was left. In fact, most of the rail amtrak uses is not owned by Amtrak, it’s leased from companies like CSX and Norfolk Southern.

Amtrak can’t simply use it because its there, and passenger trains have plenty of their own requirements due to differing safety standards. It’s unlikely that using these tracks is feasible.