The power of Reddit, my friends. Maybe someone outta throw something like Sonic Incursion or Exodus up there after people forget about this. :v:
The reason is the Wii can't handle morph targeting, and itd be much cheaper to hard swap between face models than accurately move facial points around with bones, which is what SEGA does for their games. This gives a similar effect and saves a lot of time, and its also what Smash 3DS does. I don't know if this is just Megaman, but a similar system exists in Smash WiiU, even though characters like Ike visibly move their features instead of hard cutting between expressions. Perhapse its still used as an optomization when fighting, becauee seriously when are you going to be paying attention to Ike's face when you're kicking ass? As for chosing that face, either the person found a model rigged with that expression already, or wanted to make somic edgy teh hedgy.