this only applies to France and seems to be a bureaucracy issue. At least one French SuC has now been changed from "temporary installation" to 4 stalls. Thus I'm guessing that more wil go "permanent" soon.
Our German SuCs usually have 6-8 stalls, since people from Norway, Sweden, Denmark, France, Switzerland and Austria all have to go through Germany to get to their respective holiday destinations.
I guess that's the reason for Germany's SuC density despite dismal sales...