This question holds true not only for girls, but for guys too.
When a person is physically attractive, they get a lot of attention. Even if they were decent to begin with, the attention will usually get to their head after a period of time. Now if a guy approaches a girl who has very high self-confidence, is used to getting attention, and he doesn't meet her standards, what do you think will happen? He will get rejected, that's what. Because they're too superficial and shallow. They know they'll get attention from everyone, you're just one more person adding to it. So they don't see you as anyone special, you're just another one of their suck-ups making them even more well-known.
People like that live on attention and usually think the world revolves around them...it doesn't, girls like that aren't worth it. You can find girls that are pretty AND decent too, but you are going to have to look.
Remember. You don't love someone because they're good-looking. It goes the other way around. The person that you love will be beautiful to you. If you want a decent girl, go give the "average" looking ones a chance...you might be surprised to find that they're actually better than those other bitches.