It is because of the way France treats its Muslim citizens. For a discussion of this matter and a warning to the Indian governments see Ambassador Bhadrakumar's post on his website ( ) .
Good Answer, but I suspect there is more and do not forget that if ISIS is indeed involved that intelligent minds lead the actions.
France is a late and in many ways still reluctance member of NATO and would be the first member state to see a backlash against the organisation.
In addition I can special reasons to want to ferment hate and distrust between the French majority and its large Musilim minority. Remember, modern revolution as we know it is a French construct.
If the residents in Muslim areas were to start manning the barricades in their Prefectures, (let alone declae their own Calphates within them) it would be an image of very considerable cultural significance.