The other thing that helmets/masks on characters do, is allow Disney more versatility in having the live characters walk around the park without having to fuss about with getting a person who actually looks like the actor/character, or is even the same gender, like they have to do with the Disney Princesses. Masked characters basically operate as "furries" who anyone can play.It's like becoming Sith comes with an uncontrollable urge to put something on your face and/or head
And don't forget the dark cloak.
FTR, Lord Dooku didn't wear a mask, helmet, hood, or headpiece of any kind. Nor did Ventress or Darth Maul... although with those two they have alien color faces so any actor playing them would have to wear facepaint, which kind operates as a mask when presented IRL. But for the purposes of the main in-universe issue, they are maskless.