The problem is that, historically speaking, the French monarchy is the prime exemple of how a King was able to centralize everything and kill feudality very early. While King John of England lost at the battle of Bouvines and was forced to adopt the Magna Cartha, and the Holy Roman Empire was again prone to dynasty conflicts, the french King was able to secure a demesne that is incredibly large and turn his vassals into petty subjects. This is why France was so powerful, and able to resist many invasions from other realms, despite not being a large blob.
And this is why playing France in Crusader Kings isn't really France : When you start with some post-1200 dates, the French King will have a demesne that is incredibly large, but you can't benefit from it. You actually spend a good 20 minutes on it, because you have a demesne of 19/5, and the centralization is still at its lowest :^)