It's because when people get behind a character, it's because they are cool. A puppet that shoots lazer beams is pretty goddamn cool to a lot of people. A cloud wearing pink striped pants who literally whines about everything is not going to get many fans. Granted, I liked both of them and used both on my team. However, it's not hard to see the reasoning. I mean look at all of the original SNES games. I loved Diddy Kong as a kid and all he was was a monkey in a hat who cartwheeled around and jumped on crocodiles. There really isn't ANYTHING to that but it's ****ing AWESOME. I guess my point is, character depth does not factor into popularity at all. Take Samus, or Link, or Mario for instance.
That's all fine; for an action game.
In an RPG, character development is very important. Geno lacks this. His thing is "possess a doll to complete a mission sent to him. Complete mission. Goes back from whence he came".
This is why I have a problem with Geno being so heavily requested for Smash (aside from the fact that he's a minor Mario character owned by Square and that he started as a fad), people think he's so great just because of his concept. Just because he's "cool". Just because of what he can do, people feel he should be playable in Smash, regardless of his lack of importance to Mario, Nintendo, or Square-Enix.
I would LOVE to have Shake King from Wario Land: Shake It! as a playable character because of what he can do. And to be honest, the prospect of playing as a large viking pirate that can cause fireballs to rain from the sky, fly and shoot lasers, ram into people shrowded in dark energy, cause earthquakes just by punching the ground, grab and shake people into submission appeals to me. Because I feel he's a frigging ******.
But do I honestly believe he has a shot in Smash? No. And neither should the Geno fans.
Being "cool" isn't enough.