What killed war is people phrasing the question as 'what killed war?'. Or to be more exact, what removes subscribers is some sort of mental toggle switch which has 'The best mmorpg' or 'It's been killed' and can only toggle between them, with no middle ground that's 'Hey, I like this and it doesn't matter to me much what other people do or don't like'.
It's the fiscally nasty side of aiming for a viral 'social' game, because social customers come with this mindset. Live by the social game sword, die by the social game sword.
In other words, it doesn't matter if you make great content, if you then try to attract customers who don't care about content and only care about what other people care about.