People tend to bond (marry, date, etc) others who are about the same in the looks department. Not looking the same, but the same subjective attractiveness. Beautiful people tend to fall in love with other beautiful people. OK, those of us who are not so beautiful may fall in love with a beautiful person, but such feelings are rarely reciprocated.
I read about an interesting experiment where they showed how this happens. They had a group of thirty people (sex was irrelevant) and everybody got a number stuck to his/her forehead, without knowing what the number was. They were asked to go and bond with a number as high as possible. Of course, everybody dashed toward number 30. At that moment number 30 realized that he/she was very desirable and could therefore bond with a very high number: number 30 hooked up with number 29. It didn’t take long to put everybody “where they belonged.” So yes, you’re right, we do fall in love with beautiful people, but unless we ourselves are desirable enough for them to return similar feeling, we’ll end up marring, as you say, those “who are about the same in the looks department.”