Roads are explicitly set up to be directly operated upon by members of the general public – railways on the other hand, not so much. [1] So a railway without a corresponding service isn't of much use to me as an end-user.

[1] Both because there are higher safety expectations for railways than for roads and because one of the inherent working principles of railways is to bundle individual demand into larger units (a.k.a. trains) that can be moved across the network en bloc. If everybody tried to operate their own individual little train across the network the way you do with driving your car, things wouldn't work out.