I would imagine why the popularity drop is not related to the game (it's pretty good i'd say, and not terribly difficult for f2p style game-play.. thou a bit grindy at times).
But the fact that for EU time-zones The World events occur at 2 Am and 5 AM respectively (dungeon and boss).
Which honestly leaves the EU players in the dust.. so i imagine that locks out a portion of the player-base.