Why do so many girls have such a low self-esteem?

I've met or heard from lots of them that have a low self-esteem who think they're ugly or not worth it for any man yet, WAY more often than not, they're actually quite pretty!! Even gorgeous and sexy!! And, quite often, WELL worth it for the man/men that want them!! My fiance thinks she's not enough for me but I keep telling her quite truthfully that she's the most wonderful woman I've EVER met and I'd consider myself EXTREMELY lucky to have her as my cherished wife and to spend the rest of my life loving her undyingly and forever more!! Holding her tight when she needs it, giving her ALL of my love!! She dresses quite well and is very well-kept. So far, I've never seen her looking sloppy at all!! She keeps her nails in great shape and wears very spiffy clothes! Why would she think she's not at all attractive, especially for someone that loves her as much as I do?
I just think it's so self-harming to keep putting yourself down!!! Especially since there's nearly ALWAYS gonna be SOMEONE else around to do that for you, at which point, you're ready to fight them!! Well, if you think you're better than what they say and pretty enough to wanna fight over it, why would you think you're NOT as pretty as you ACTUALLY THINK you are?
I've had a number of people in my life tell me that I'm ugly but, I never thought I was. I wouldn't consider myself an extremely attractive guy but I have yet to have villagers chase around with torches and pitchforks!! I know of one girl that actually told me that I look like Fabio! So, how ugly could THAT be?
Anyway, I just figure, I'm me, there's not a fucking thing anybody can do about that and if someone doesn't like that, that's THEIR problem!! NOT MINE!!! So, if they're gonna say I'm ugly, why should I do it, too? And, most often, those kinds of people don't know their hole from an ass in the ground!!
Honestly, I don't care HOW my fiance looks!! I'm in love with HER!!!

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She's got the most beautiful soul I've ever known and THAT'S what I'm in love with!!!
Why do so many girls have such a low self-esteem?
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