Several reasons:
#1 - Don't have spare cash and would rather spend it on PC games or save up for next Nintendo Console since the new Smash Bros. would be released on that.
#2 - It's a remake machine and that's about it. I have yet to see one original title or new title on the handheld yet. And I'm completely disappointed with the Ocarina remake. It isn't the best Zelda game, and even if it was, it's not worth me shoveling out another $40 just to relive the experience again when it is already on the N64, Gamecube, AND Wii's shop channel. I'd be more interested in a game that hasn't already been remade a billion times, like Final Fantasy VII... and I hate Final Fantasy.
#3 - 3D is a gimmick and nothing more. If I buy the system, I'm folding on this belief. I'm pretty much saying that I give in to the 3D craze that has hit hollywood, Nintendo, and Sony (tvs) by storm. But I refuse. I'm not paying extra money for movies or games simply because the quality is supposedly slightly better.
#4 - Why haven't we released a new StarFox, F-Zero, or Fire Emblem game yet? You're back to remaking Zelda. Pokemon has already mentioned they're in the works for a 3DS title. Mario will no doubt rerelease Mario Sunshine for the 3DS. But why haven't we even seen anything for a NEW one of these guys? I know they are not your big sellers, but they're better than Mario or Zelda anyway. Also, when is Mother 3 going to be released outside of Japan?
that's about it because my food is getting cold and I'm tired of ranting.