It is sad I know.
But from my understanding it is lack of community. Yes there is a very solid core base, but it is small. Not enough people were playing the game for it to be worth it to keep the servers up.
I wont go on to say maybe it was lack of support and the fact no one could find cards anywhere and because of high prices of cards and expansion packs...but I won't be argumentative and get into those things and say them....heh
So yeah not enough poeple playing.:-(