[amqvexxv] Be a good girl

Two of the most popular songs of 2013, Robin Thicke, et al.'s "Blurred Lines" and "Let It Go" from Disney's Frozen, share a common theme:

I know you want it / But you're a good girl

Be the good girl you always have to be / ... / Let it go, let it go / That perfect girl is gone!

What does it say about society when songs decrying the social obligation to be a "good girl" keep becoming popular?  Exactly what are those onerous social obligations?