maybe you arent friends with any girls? Friendship is the best way to begin, relationships are so much better when based on friendship.
Also, has it occured to you that if alllll the girls have boyfriends, accoring to you, there cant be many men left over to be single! (the difference in gender percentages does exist, but it isnt huge) so unless each girl is sharing her man with another guy, this dosent make logical sense. Im sure it just seemes this way.
Stunning girls, plain girls, all types of girls, have different personalities. You get girls who are incredibly pretty but still have lovely personalities, girls who are slightly plainer but their personality makes them have a lovely smile, or escence to them. You'll get beautiful girls who are vain and mean, and plain girls who are nasty too. I personally wouldnt pick a relationship based purely on looks, so I dont think you should be so shocked that plainer people get partners too!