Why would someone call me ugly anonymously?

So someone has sent me an anonymous message saying " Why do you act like you are all that when you look like that? You are not that beautiful and i am sure that all the complemets u receive are your fake accounts." I don't know why would someone think this bullshit. I would never fall that low to do such thing and this shows how insecure that person is. Why do you think someone would go and write something like that?
Why would someone call me ugly anonymously?
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