I'm a fan of more realism, but I know many people want to play beautiful people for some reason, even though no adventurer would look good very often, what with the injuries, dried gore on their armor, etc. Their aesthetic ideal of their hero is without a helm, however unrealistic it is (at least I am assuming this is about aesthetics, which strikes me as a safe bet).
I think what we need to understand about helmet-hiders is that they go for aesthetic ideals instead of realism.