It is about expansion. All you need to do to get that copper patch is extend the network from your nearby coal patch and build a station. Whereas you might need many thousands of belts to do the same and you wouldn't be able to share the existing infrastructure of the coal patch (unless you really like sushi as well as spaghetti).

Honestly? There isn't much point.

Rail really starts to shine when you've exhausted a few ore patches and it's much more relevant on railworld generations where you have large gaps of mostly nothingness.