I agree with where the guys are coming from here that hair is what makes someone attractive to many people. When I tie my up I think I look ugly but when I have long straight hair it somehow accentuates my features. Also if my hair is messy I think I look ugly but if it is nice and straight and flows well, I think I look pretty. I would imagine it must be a similar thing for what guys find attractive.
To be honest it is also probably a bit to do with society's views on what makes someone feminine as well. They may be preconceived ideas of what feminine is, but nevertheless most of society agree with those and that will affect people's views on what is attractive.