Why do people say that dark skin girls which they were light? ?

I am a dark skin girl I am kindof short,big brown eyes,medium nose,medium size lips(a little plump),dimples,slim.Lots of boys like me(and no it is not because I give them sex,I am waiting until I am married to do that),even the dark skin ones.I have never experianced discrimination based on my colour and noone has ever told me that I am pretty for a dark skin girl,they just say you are really pretty and some tell me that I am prettier than beyonce').I do not wish I was light skin,I love myself!I love my chocolate brown complexion.I have no envy for my light skin cousin,who is also very very pretty and lots of boys like her also.So why do people say that dark skin girls have low confidence and are potrayed as ugly,never happened to me.