You have to compare MMO's with MMO's (other games have different activities in long term play) and as such an MMO without a subscription only took 40% of player actvity compared to a game with a 180 dollars yearly subscription.
That's telling everything really. So how would you explain that a game within the same genre that's buy to play is far less popular than a game which costs at least 4 times more to keep playing, probably more over several years.
Essentially it means that the MMO's no longer evolve, because WHAT would be the player base if GW2 even had a subscription...