Because, you can liken LoL to Chess. It, in a sense, is a more dynamic game of chess. While it's true that Chess can be played for fun, and it often times is, you can't ignore the fact that the fun of the game comes from the challenge. With that challenge comes a sense of seriousness to make the game fun. It wouldn't be a proper Chess game if every grandmaster out there went willy-nilly with their queen, nor would it be much fun, for anybody.
When you run stupid shit like say AD Lulu, it's good for a few shits and giggles, and to see where the game can be taken, but if it doesn't go well,or if it messes with the way the game's known to play, it's not fun for the others involved.
Have your laughs, but don't take them seriously, and sure as hell don't make it the norm for when you play.