> Unlike in much of the rest of the world, the United States’ rail network is fragmented. Rather than having a national railroad, or tracks open to use by any company, our railroads are vertically integrated—they own, maintain, and run their own lines, and compete largely on the strengths and weaknesses of their networks.

For what that's worth, that used to be the case in many countries, it was certainly the case in most of europe before the inter-war period (e.g. the ancestor of Deutsche Bahn was created after WWI, the french SNCF in 1938, and British Railways after WWII).

And numerous traces of that remain if you know how to look. Paris has several major railway stations each serving a slice of the country (and inconveniently disconnected requiring connecting transit through the city) because each of these slices used to be handled by a different company, each with its own terminus station in Paris.