It was announced during Nintendo's E3 Direct that Miis have been added to the roster for Super Smash Bros. on Wii U and 3DS and now series creator Masahiro Sakurai has explained why in his Weekly Famitsu column.
Sakurai revealed that incorporating Miis was considered for Super Smash Bros. Brawl but he found it hard to imagine them fighting and there were fears that incorporating Miis could lead to bullying and so he decided against it.
"Incorporating Miis was explored in the previous game, Super Smash Bros. Brawl, but I thought it over for about a minute and immediately decided against it."
With Miis now being used as personal icons and the first thing people see when they turn on their Wii Us and given their expanded role, Sakurai felt he could no longer overlook them for a place in the Super Smash Bros. roster.
"We don't want the online play to become a copyright free-for-all and it's probably not as fun to play against someone using a character based on someone you may not know."
Due to the aforementioned bullying concerns, Miis cannot be used for online play.
Ultimately, it was the volume of requests for their inclusion that swayed Sakurai's hand. Many frequently requested characters cannot be featured in the game due to copyright concerns and development cost but with Miis, players can create characters to look anyway they like.
Super Smash Bros. is coming to 2DS and 3DS on October 3rd and to Wii U later this year.