Never played Farmville, but I'm guessing part of the stickiness of the game was the slight but not insignificant emotional pressure of seeing "<your friend> wan

Never played Farmville, but I'm guessing part of the stickiness of the game was the slight but not insignificant emotional pressure of seeing "<your friend> wants you to plough him/her" or whatever the notifications Farmville sends out actually looks like. :p Without that slight pressure of seeing your friend asking you for help or collaboration or whatever, it's probably become much easier for people to not play that game.