alt Hacker NewsRailroads are a natural monopoly, as are highways, power lines, last-mile internet, etc. Once you have a railway in place, it is rarely profitable to have a single competitor, let alone the three or four you would need for a genuinely competitive market.
Railroads, like airliners, form a network. There are multiple paths to the same destination. There are also competitors in the form of waterways, air corridors, and highways.
Before the government began regulating the railroads, this is exactly what happened (though no air corridors then!).
Power lines also form a grid, and can route around failures. The power to my house got a lot more reliable when the other side of the neighborhood got connected to the grid.
When the power does go down, so does the cable internet, but the internet still works because the cell towers take over the last mile traffic. There's also Starlink.