Because, I want certain characters to leave because they don't bring anything new to the roster.
Young Link - Clone, and he looks so much like the normal Link, that it is sometimes hard to distinguish between the two characters.
Pichu - Clone, and it hurts itself, so it is already an extremely poor character choice. And, we have Pikachu, who is an original, and is its evolved form, AKA, it's upgrade.
Dr. Mario - Clone, and he is Mario in a different outfit. We could have included him with a costume change like the Peach/Daisy deal.
Marth and Roy - OK, this one is completely biased of me. I just think Ike and the Black Knight would be much more bad*** and cooler replacements, and I never had a strong liking for these two characters, they don't have a lot of personality.
So, IMO, Pichu, Young Link, and Doc NEED to leave.
But Sheik, I didn't mind. I mean, she was extremely overly powerful and unfair, but if she gets nerfed a little, she is still a cool addition.
People also seem to think that Ice Climbers and Mr. G&W should go, but they are two of the most original characters in the game, and they were a ton of fun to play.