After dozens of laggy as hell online games in LBP, unless there was some way to guarantee lag free play, it would be a disaster online. Not to mention that Mario platformers require more precision than LBP does.
Don't get me wrong though. LBP is a lot of fun, but unbearable lag kills the fun faster than anything else.
I do this Nintendo should have done online leaderboards though, and had challenges with online rankings. Something like that would have been a good and obvious addition to an already excellent game.
Demon's Souls Official Thread | Currently playing: Left 4 Dead 2, LittleBigPlanet 2, Magicka