They're not, it only takes 30 seconds to make a mii fighter and players will just make them on the spot when they are needed. I'm sure that all 12 of the possible movesets amongst the 3 mii fighters won't all be made. So just make them if they're needed and they're already not there. As for the rest of the customs, that still requires the use of the 3DS, requiring the TO's to take the time to put them on every single wii u and to have a 3ds with all customs unlocked. I honestly think thats something we should push for next year, but at the very least letting the characters that have their moves already unlocked choose from 3 different loadouts is good enough. Honestly, as long as every one of their customs just gets to see the light of day in some form or another, its good. I think its an acceptable agreement for now.
Again let me restate why this was accepted, instead of it being viewed as only mii fighters getting custom moves, its actually just increasing the roster size from 51 to 60. Start mixing and matching and it becomes too complicated, at least for right now.