Why do nice guys finish last?

I have a friend who is a girl and who has also told me several times she would say no if I asked her out. I asked her why, and she thought about it and couldnt think of a good answer. I have a great personality, everyone likes being around me (including her) I am reasonably handsome, I have a good job, it seems like I'm doing the right things... The last time I asked her and she said no, 2 days later she started dating a guy who is OBVIOUSLY bad for her. Like literally every single person she asked said he is bad for her. I truly do like her and want the best for her, but she won't listen to anything I have to say because she gets all defensive of her new boyfriend. I have asked all my friends if there is anything I should change so girls like me more, and none of them could think of anything I should change. I dont get it, if anyone could help me, I am open to any criticism thank you, it would be appreciated.
Why do nice guys finish last?
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