There's a ton of reasons why/how a girl could LJBF a hot guy...
Having a hot guy as your friend can be social proof just like having a hot girl as your friend is.
I think there's more to "relationships" than just looks... if someone's personality doesn't "do it" for you, then you wouldn't want to date them. Someone might have a great personality as a friend, but you couldn't feel more for them, regardless of how they look.
There's also a difference between finding someone hot and finding them "attractive". I think Jenna Jameson is hot, but would I **** her? absolutely not. I'm not attracted to women. But is she hot? Hell yeah. There's a difference between finding someone aesthetically pleasing and them turning you on.
Sometimes there are other factors... her best friend likes you (or used to like you 13 years ago, sometimes girls are very loyal regardless of logic) so you are eternally "hands off" no matter how "hot" she thinks you are.
Or maybe she has a thing for one of your good friends. Even though she thinks you're all good looking, he's the one she wants... so all his friends automatically go into the friends zone.
She's seen you hook up with a ton of girls (or even worse play/cheat on girls) so even though she's your friend and thinks your hot, she would never ever be your girlfriend or hook up with you because she's had an inside look at what that would be like.
Or maybe she just knows that you two are looking for different things (ex. her a boyfriend, you a quick lay, or vice versa) so she doesn't want to get involved despite how "hot" you are.
She might have seen you in some way that totally turned her off to you sexually, so even though she knows you are still "hot" and likes hanging out with you, etc, she doesn't see you sexually (anymore?)... This could be anything, saw you puking after a party... saw you dance... anything... girls can be pretty fickle. Once I had a crush on a guy for almost a year until I saw him playing guitar and something about the way he moved with the guitar made me laugh so much, I was turned off forever after that.
She might have wanted to **** you in the beginning of your "friendship" (sometimes it's true, a male-female friendship can be just a front for "I'm gonna get them eventually") but then you either got stuck in the friendszone or one of the above things happened... so now you're her friend. Period.
If you guys ever did have a fling and it was bad and you don't want to do it again... then you're in the friends zone. Or even if it wasn't bad, but you both know it wouldn't be a good idea to do it again, then you're in the friends zone. A lot of people don't think girls & guys can be friends, especially if they are exes or hooked up in the past... but a few of my really good guy friends are people I hooked up with... Not sure if they became such good friends because we hooked up, or if we hooked up because they were such good friends.
And there's a hundred other reasons why..........
One last one for now: Maybe she doesn't really think you're hot. Here's another secret of the female gender: sometimes we lie. It could be to spare someone's feelings, it could be to be cruel, it could be to help ourselves in someway... Just because you think you're hot or someone tells you they think you're or sometimes tells you "she thinks you're hot"... doesn't necessarily mean you're actually hot. (I'm not implying YOU aren't hot

... just saying, that's another reason right there).