Why is that some attractive/hot/good looking men and women single?

I’m not saying all of them more but I read and heard that their relationships don’t even last and some in up in a divorce. My dad always told my sister and I to never go for the hottest or most attractive men because they’ll make the worst parters. Let’s face it, none of us wanna date an unattractive person. He even told my brother to stay away from the really gorgeous girls.
I’m at there’s nothing wrong with eating them as long as they have a good personality.
My sister says she rather date nerds than a hot guy because she dated a hot guy one time back in high school and it was the worst because all he was about with his looks and girls were running after him. I have a cousin that’s very gorgeous and she is so stunning but she’s always single. It’s like every time she’ll come she has a different guy that she’s with or she gets dumped or she dumps them. I’m sure she’ll find the right guy. I said the guys don’t approach her.