The problem is that Paris isn't a hub: it is supposed to be everyone's destination, so there is no need for transfers! So they have what we call "head stations" in Dutch: train stations where train lines begin and end. We have very few of those: e.g. most intercity trains arriving at Amsterdam CS will continue to some other destination opposite to where the train came from.
But Paris is mostly like that (only the eastern TGVs don't require taking a metro to continue: they stop far away from the inner city, at the eastern aeroport, then continue south).