1) Engine sucked balls. One of the worst engines to ever host an MMO. Period.
2) Touted "EPIC NEW COMBAT SYSTEM THAT WILL REVOLUTIONIZE THE MMO GENERA" turned out to be the most horrid combat system ever devised.
Those are the 2 main reasons AoC failed hard and Funcom is now called "Failcom". I cant believe they have the audacity to make 'The Secret World' and think that people will purchase it after they fumbled the ball and lost the superbowl in the last 15 seconds.