I kind of feel sorry for actors who are cursed with physical beauty. I think the producers thought that was enough. Well, indeed it was from a business perspective... the movie made a whole lot of bunch of money. I've seen Jessica Alba in more than one movie and I have to say if she took on a much more serious role, I won't hesitate to see her perform. So much potential. Same for Paul Walker.
Plus, I get this impression, based on interviews and their "public persona", that these actors do not really want to be sex symbols. I have no scientific explanation for that, just this general impression. "Pretty Boy" Paul Walker went to college, by the way, and majored in Marine Biology. Nature lover, that guy. Also, he has said in an interview (I did not read this somewhere, I watched him say it) that he auditioned for some roles to pay off student loans.
Jessica Alba leads a life that's not quite sexy by today's standards. You never really read anything about her sleeping around, partying. She married a pretty decent guy, is a devoted mom of two and occasionally has dinner with herself (yeah, explored her twitter). Yawn, tabloids.
Yes, I thought about these things today.