That's correct. But as others have noted, Paris is the "center" for most anything. There's very little demand for travel between any pair of two (major) cities other than Paris.

I should look this up for details, but I seem to remember that there's a train route running parallel to the southern border that was abandoned for lack of demand. And there are some major cities there (Marseille, Montpellier, Toulouse) which aren't all that far apart.