SonicMario
Smash Master
They don't have to care about the Mii. Much like some could not care for Pichu or Dr. Mario when they were in Melee. Or if there's anyone playable in Brawl that someone dislikes as a character, they may not like they're on the roster, but they don't let one character being included ruin the game for them. But for those who don't mind the Miis, or even like them. They're just another spot filled in by a Nintendo owned character. No big deal.Second: Logically why would people who up to this point only played games with defined characters and art styles suddenly care about the little rayman knock off people that look like they came from a gamecube tech demo?
There's plenty of things you can give the Mii in movesets from besides Sports equipment. As there's more then just Wii Sports & Wii Sports Resort. There's some quirky stuff you can borrow from some of the games of Wii Fit, Wii Party, and even some stuff about the Wii Channel itself that Bluepikmin11 brought up for example. Miis don't necessarily have to be customized in Moveset. Considering Sakurai has made a race car driver & a NES peripheral into capable fighters though. This isn't really much of a factor, If needed Sakurai can make stuff up that's still creative enough that it seems natural with the character.Another bit of logic: In gameplay what would they even do? Sports equipment? With no voices? Do they have arms or not? Do you customize? If not who's to say what a mii even looks like? It's more trouble then it's worth.
Easy answer to this: Brawl was not focused on representing the Wii too much other then the fact the game was on the Wii. Sure there's references to Wii games within the Music and such. But the newest character by series was Olimar, which started on the Gamecube. While the newest character overall was Lucario. Who hails from a predominantly Handheld series. Brawl focused on celebrating the Gamecube generation, which the Miis were not at all a part of. Much like how Melee did the same for the N64, and SSB64 did for the SNES. As such, SSB4 will be celebrating the Wii generation. Most of the newcomers so far reflect this. (Wii Fit Trainer = Wii Fit, Villager = Default look is the City Folk design on the cover, Rosalina = Super Mario Galaxy, Little Mac = Punch-Out Wii)Another bit of logic: Brawl didn't even have a Mii trophy, not even a sticker. The only references to any Mii were a few songs on Pictochat. There's no logic leading up to the reveal, the other new characters (Barring Mega Man and characters that didn't exist before Brawl) are all characters people expected based on appearances in Brawl.
Miis were an essential part of the Wii's success. There's no denying that. The Top 2 selling Wii games of all time are Wii Sports & Wii Play. Albeit the former kinda cheated in that it was packaged in with most Wii consoles, Wii Play was not. Right below them at the #3 best selling Wii Game was Wii Fit. And look who we have on the roster already: Wii Fit Trainer. It's safe to say with Wii Sports, Wii Play, Wii Fit, and Wii Sports Resort taking nearly half of the top-selling 1st Party games, that there's a pretty strong case for Nintendo to include them this time.