Firstly, Game and Watch did absolutely look like Game and Watch in his games- they may have refined his details, but that is true of any character, and legitimately necessary for any receiving as harsh of an upgrade in pure pixelation as he did. He was clearly recognizable from those games. The Miis, conversely, not only look differently every time, but that is their schtick- I'm not claiming that
The Miis additionally, are not even the Stars of their franchise- they are merely avatars of US in their "franchises,"
To even call a franchise is a bit frivolous, the games have absolutely nothing to do with each other mostly, and just use the concept of the avatar character. Again, other Nintendo IPs are notorious for this too, but at least they are a stable Property, with some amount of design, relationships, development at all. The Miis have none of this, they have simply a name, and the fact that they are visual representation of us in game That isn't an entire WORLD in a game, sch as Mario or Zelda or Starfox, it is a brief concept, utilized as loosely and far reaching as the aMIIbo. The whole point of the Mii is just to make an experience personal; it may be a copywritten word and Idea, but they certainly are not a franchise; even in Smash, they aren't a franchise- we have all of the Mario subseries (Kart, Paper) lumped together, but their games are separated as far as getting different symbols per game, because the Miis aren't the star.
All this said, the Miis are important to Nintendo, but they are not stars in their own right. You could not have a Mii at a meet and greet, whereas you could have any other character, even Villager or WFT.