Those kind of girls never grow as people because they get all their validation from guys that would tell them anything they want to hear just to get in bed. I also think that in the back of their minds they know this to be true and its the reason why beautiful women are so insecure but its not all good looking women and a lot of it is the men fault for treating women so well, kind of like a parent that spoils their child, most men let beautiful women get away with murder.
Not all pretty girls are conceited. There are a lot out there who are beautiful and think they are ugly... and are very humble. It's all in the attitude of us women. Some may appear to be conceited and are the total opposite. Your question is almost like saying why do hot guys only want skinny girls! And we know lots of hot guys like their women any shape, as long as they carry themselves with confidence
good looks are an advantage in this society. the better you look, the better you get treated. don't believe it? stop taking care of yourself for about 3 weeks, have messy hair, out of style clothes and leave the house and see how people react to u. then amp up ur program and look really good leave the house and compare the difference in how people react to u.
girls can become overly confident because society puts them on a pedestal and its almost like being treated like royalty. *BEAUTY QUEEN* *HOMECOMING QUEEN* *PROM PRINCESS* for example...guys are super nice to you because they want to impress u, girls suck up to you because they want to be like you and get some of that attention to rub off on them. so some girls can become conceited as a byproduct of society...for the flipside many unattractive girls can have low self esteem