Why not I mean if they keep the vanilla expansion forever players might get bored from doing the same thing every single day eventually players will leave and abandon the server for the lack of contents so if they bring a new expansion every year or half year might get players excited and new players will join in or simply all players will get bored and leave the server so bringing new expansion is a good thing ( pardon me but I never played this game but it's a logical thinking lack of content in a mmorpg game means loseing players till nothing left )