It's novelty wore off once people realized that nobody made any levels that were actually fun to play. Also, the actual mechanics of the game were terrible. Horribly slow for a platformer. I'm pretty sure I have played atari games with a knock off joystick that felt smoother than LBP. I'm getting angry just thinking about it.
Edit: Also, the art style. The sackboy looks awesome, but the environments look terrible, the collectibles looked aweful and weren't fun to collect, and nobody wants the damn stickers. I better leave before I say something I regret. I just really hate LBP.
"Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth." -My good friend Mark Aurelius