I'm always the wrong guy to ask as a customer what business model to use to make money, but I remember reading some Call of Duty required people to buy maps or else you couldn't join multiplayer servers with them. There was a lot of predictable complaining that there weren't many players on the servers using the new maps. It honestly sounded exhausting to keep track of as a player to me and like it would server to repeatedly split the player base until the population died out.