>>13794Dunno about France and their system, but the idea behind it in America at least is that you don't have the nation's politics ruled over by a small geographical segment of the nation. The population centers, in particular.
Fundamentally, there's no point in being part of a nation where you've no sway and they don't hold to your interests, after all.
If you want to keep a republic together, rather than only controlling those smaller but high-population zones, you're going to have to do something like this.
Else you inevitably get uprisings, rebellions, and the ilk.