It was pretty buggy anyway. Voting was useless and gold wasn't saved. The concept was good but the quality of the game wasn't.
Blocks & Zombies was at first a game mode, but when they added in a variety of mini-games, Blocks & Zombies was added to the mini-game list. It was a very popular game mode, but when that happened people stopped playing on it. It could've been removed because no one plays on it or as other people have said, the plug-in wasn't working properly.
The only thing wrong with the game-mode was that my vote rewards never worked properly. I for one actually enjoyed playing it when it first came out, I even managed to get myself on the leader signs for a short while.