The trouble is that the cartographers only know so much about the roads. They know where they are but how can they know the current condition of the road? Keeping in mind that most of these maps are at least several years old. Some private roads aren't known to be private by the cartographers either.
This just illustrates that the GPS is a tool. You wouldn't allow a circular saw or a chain saw to just go where it pleases. Likewise you need to understand your tool and augment it with other tools, paper maps, advance research, etc.