Because what others can't control they try to manipulate through name-calling.
There is a difference between being a "prude" and not being easy. A LARGE difference, actually. A prude is someone who is EXCESSIVELY proper or modest, in speech, conduct or dress; a girl who ISN'T easy just has high standards. Don't confuse the two.
Same thing as calling guys studs, when they're definitely not horses!!! ;)
whos side you on man?... i don't call em prudes i call em teases ;)
This is because they are called prudes by two types of people. One: guys who WISH the girl was easy. Two: girls who ARE easy and want not to feel indecent or abnormal. Three (bonus): by people unfamiliar with what sexuality in a certain culture is.