Often times when female celebrities appear at the Oscars or some place similar, they pull their hair back in a “pony tail” or bun. Therefore when you see their face straight on, you only see face with a little hair on top.
Most are younger females with a great head of hair that would “frame” their face beautifully. Many have attractive faces, but why don’t they use their gorgeous hair to enhance the beauty of their face? Why hide it behind their head?
The more mundane answer might be that they have really zealous hairdressers who are mandating an “up-do” for any special occasion. This is just a guess…
Because it’s hard to look elegant with stray bits of hair falling into your eyes, getting up your nose, or otherwise floating at random around your head. A tight, pulled-back do is less likely to be disarrayed by wind or long nights.
Yes, they know they look attractive with the hair framing their faces. They may also want to keep control of their potentially fly-away hair without having to spend half the night in the ladies room brushing/combing it back into shape.
For the same reasons that less famous girls put their hair up for prom, weddings, dances, social functions: it looks clean, classic, and it’s out of the way. Just because they’re pretty and famous doesn’t mean they wouldn’t/shouldn’t conform to the social precedence/beauty and fashion norms.
Because they’re wearing fancy gowns, and when you wear a gown, you wear your hair up. That’s the social convention. I’m sure that they let their hair down when they change into their little black dresses for the parties afterwards.
Also, a lot of women think they look more attractive with their hair away from their face.
I get told time and time again that I should grow my hair long. But I personally think I look ten times better with shorter hair. I think it’s because I’m primarily concerned with my face, where other people are interested in the “overall sexy” effect.