I can personally say that it might not be that white people are prettier per say, but that straight hair is seen in the media as the in thing, from what i gathered. And most teens, and young adults want to be "in". Me i personally don't care at all, and have a tendancy to let my hair be wild and crazy when it feels like it. One girl asked me in stagecraft a few months ago wether i had ever had my hair permed straight. I have and i told her so to her face, i also got snarky and said i was going for a suesey sue & the banshee's look. Right now my hair is short and permed but im growing it out so that i can get my healthy crazy kinky hair back.
My mom is mixed European,Native american,asian, and middle eastern. And my dad is African american, and native american. I find my kinky hair to be beautiful, if a little annoying at times. Some people in my family say its thick and nappy, but i cant say i really agree. thick yes, but then again my grandma on my moms side had thick wavy hair until the day she died, so my hair is naturally quit thick. I'm firmlyconvinced its genetic!
The whole straight hair craze might just be about wanting more "managable" hair. I'm not completely sure but thats were my thoughts have lead me.