As a very general statement, military areas are rarely actually active but (esp. in France) the military tend to pretend they are active because they know they will otherwise eventually lose them. So ATC will keep you out of there even if there is no real reason.
If you look at the airway network, you see how the military areas define where the airways go (or vice versa).
If the military areas were removed, the whole low level airway network would be transformed.