Blizzard completely stopped making single player games (until Diablo 3) because of WoW's unprecedented success (quite a few other games were cancelled to keep this machine running).
LoL and DotA 2 are similarly addictive since each game nets you drops, some seasonal exclusive cosmetic items, couriers, etc. They also have challenges to keep you coming back.
They're explicitly designed to draw the player back and get better, a fallacy since a player is only as good as his (current) team. So these games usually have a bunch of people who hate the game (Griefers) yet keep playing to grief others with relatively better success.
I'm of the opinion that games without intellectual value must be avoided. And I was a semi-professional gamer (COD & DotA) for a while. One of the best games I had played that were short yet memorable would be the Age Of Empires series, Braid, Hotline Miami.