The reason this game has lost so many subs is because of the sheer amount of MMOs out right now. None of them are bad but, none of them are great either, and it's spreading the populations among all of them pretty thin. No game out right now has a monster amount of subs.
Have you lived under a rock these past 8 years? WoW has the must subscribers in the entire mmo scene (Paying customers, runescape not included).