Because they have low self-esteem.
I believe it's frustration/anger..no matter what they do they never feel improved. They need constant change to get satisfaction in the mirror.Even beautiful people can have these beliefs. Very sad and some die from it.
Because: They want the same thing as everyone else, but always find themselves out of the room. <br />
Who can they blame if no one is around?
Ugliness doesn't make anyone a masochist .... maybe it does if you always want to be punished if it's your fault. My worry is that it does make "ugly" ones a sitting duck for the first predator who shows some interest
Consider the culture... advertising in particular. Have you ever seen a commercial laced with half-dressed people, and that has NOTHING to do with the product?
Low self-esteem, they will treated their spouses as mean as can be because ironically they want them to stay....I've known several gorgeous women who had some homely husbands and it seemed to be a pattern in their marriage.