The game has been kinda dead for a while now, because it's so unaccessible to the general population. Games like Dota and League of Legends have taken the place of Starcraft 2 because it's pretty accessible to newbies yet offers a very high skill ceiling for those who want to play competitively. Starcraft 2 is simply too difficult of a game - you have to micromanage not only whole armies but also create new buildings and new units, looking for ways to boost your economy, and micromanaging research, all at the same time. It's simply too much to ask for a new player looking to break into the game.
Dota existed because players just wanted to play a single hero inside an RTS game, and not have to control an army. The army is automated, there is no research, and there is no building/economy to worry about. You simply control one unit. Then League came and made it even more accessible to new players. Starcraft just simply cannot compete with both of these games, it just takes too much effort to even be remotely good at the game.