Well not all of us wore hats on the other races. I almost always had a flower in my hair as a miqo so that means the hat restriction on viera doesn't affect me much personally. However just because I rarely wore hats doesn't mean I don't want other players to have the option to. I know some people who won't play viera and hrothgar solely because they would no longer be able to wear hats.
My personal issue is hairstyles. I love the one I have...but it's the only one available I like for my character. To make things worse the hairstyles I used on my miqo would need minimal adjustment at best for viera. Viera and hrothgar have a ridiculously low range of hairstyles. If we can't have hats at least we should have a lot of hair options...but we don't : /
When you look at the whole picture viera and hrothgar have by far the smallest amount of head options by a huge chunk compared to the other races, because they got shafted for both hair and headgear. And on top of that hrothgar need to fantasia to get a totally new hairstyle which is just...wat -_-