Why don't boys fancy her?

One of my friends called Abbie is just amazing. She is absolutely gorgeous, lovely, smart, bubbly, cheerful, friendly, funny, always smiling and everyone really likes her. She has loads of friends, both boys and girls and always gets along with everyone :) sometimes I get a bit jealous of her! Hahah ;) as far a relationships are concerned, she's had two or three but since starting high school, she hasn't been out with anyone. She has been asked out a few times but hasn't been interested in them so she let's them down gently. She isn't a slaggy, showy, slutty kind of girl who is easy to get. She's more of a friendly, pretty, hard to get girl who gets along with everyone and is always laughing and smiling. She has a lot of friends who are boys and they are always coming up to her and chatting to her. Some of them have told her that she's gorgeous but as far as I'm concerned, none of them have actually made the move to ask her out. I once went on her Facebook and about 5 boys have been inboxing her daily and I think that there is a possibility they are intrerested. Our other friend Chloe is pretty but a bit on the slaggy side in the sense that she is always flirting and wearing skimpy clothes with tons of make-up. She is easy and flirts with anyone whereas Abbie is particular about who she flirts with but seeing as she's so funny, she's always having a laugh with everyone :) lately, Abbie's been down because she feels that boys are only interested in her friendship and she feels like she must be doing something wrong for them not to be asking her out even though she is so liked by everyone. Does anyone have any ideas why all the boys seem to be interested in Chloe and not Abbie? I just want to reassure her that she is amazing, no matter what. :')