Most likely because he is so friggin' cool.
Besides, this clan isn't too popular yet, so I'm not sure why you are even posting that (and especially why in this thread).
He is a good character. If anyone wants proof of that, I will fight them (assuming they have Brawl like me, of course). Actually, saying he is a good character is a moot point, as all of the characters have been balanced so much that everyone of them can hold their own.
I am getting sick of people saying that a particular character isn't good when the sole reason is a different play style than what that person is used to, or just plain not liking the character. I think Wario is a 'bad' character, but that is only because I don't know how to use him. Anyone who mains Wario will say that he is good. Why? (You guessed it: They know his play style and have had experience playing with him!)