Maybe you don't want to have all kinds of unwanted attention and weird interactions about your physical appearance. Or risk some psycho harassing or threatening you. Or your boss not agreeing with what you say. Same for some family members.
How many very attractive women try to uglify themselves in order to avoid all kinds of shit?
Let's not talk about shyness or social anxieties.
Being famous is not everyone cup of tea. Many people would really, really hate it.