They obviously don't ask for native French speakers because many, many, many, many, many, many CMs in all types of jobs are not native French speakers. They do speak French, to some degree (be it fluent or just conversational), but they are not natives.
I don't know in other countries, but when I've talked to people who have been hired by DLP in Spain, they always said knowing French, even if it wasn't completely fluent, helped, but they'd rather you spoke English fluently. After all, you'll be in France, working in a French environment, so they thought your French would get better once you moved to France. Of course, if your French is terrible, they probably won't have you working at, let's say, the ticket counter or City Hall's desk.