I think that's part of the reason ED is now allowing skilled mission makers to publish their missions and make money. That way there will be way more campaigns available to be spread along the different maps. But it's a valid concern given how soon there will be 5 different maps already (leatherneck's map that comes with F14, NTTR , Caucasus , Hormuz and Normandy)
But the opposite logic also applies. If the devs spend more time making campaigns for the new maps , people will be more inclined to buy said new maps.