normally there are only 2 major reasons: -

a) over-confidence: always believe in better is out there, rejected all the possiblities when new guy come along. If you belong to this group, wake up gal. Every human has flaws. Perfect man is not going to happen, ok? Settle down in a short term relationship won't hurt much, at least you got to learn how to improve!

b) short of confidence: why would guy want a gal who do not even like herself? the ugliest and fattest gal i know also got married already, i can't really think if there's anymore gal out there guy will not love. Do not be the one who convince guy you not worth the love!

Wish you all the luck with love!