In a statement posted to MLG’s website, CEO Sundance DiGiovani stated

StarCraft 2 is a real-time strategy game developed by Blizzard Entertainment released in 2010 along with an expansion, Heart of the Swarm, that was released in March. Blizzard is also the studio behind World of Warcraft, and like WoW, StarCraft 2 has a very strong community behind it. John Bain, aka “Totalbiscuit” spoke out to PCGamesN on why MLG got out of the World Series Championship due to some restrictions imposed by Blizzard

It is very unfortunate news for people who train and dream of being in MLG and not know if the game you practice will still be a featured title.