Danielle Egan, Professor of Sociology (thank god not Economics), wonders aloud in a Watertown Daily Times article: "Why do we live in a culture where if a woman shakes her groove thing, she makes more money than an elementary school teacher or an administrative assistants?"
I could snipe at the construction of that sentence, but it's from an interview, and I know how easy it is to say silly things in an interview. So, not to be mean, but she could always go live in a different culture if she thinks it's that wrong.
Her question has three answers. One is really cheap and goes like this: "Just cuz". Why does anything cost more than something else? The exact answer to price differentials in labor is incredibly complicated and probably has something to do with the price of tea in China. But that's the cheap answer.
The less cheap answer is to hold jobs constant and vary labor. Who fills what jobs? We could choose them at random, but Danielle would probably not be the best professional basketball player since she's probably not seven feet tall. Not every person that tall is necessarily a good basketball player, but at least they have a chance at it. What if they'd rather be a professor of sociology like Danielle? How would you convince them to make use of their special gift of height? Answer: by paying them lots and lots of money.
Getting closer to the topic at hand, not every woman is well-suited (get it? Well suited?? Well birthday suited? Hahahahahahahahhaa!) for that job. Only a fraction of all women have the ability to make money taking their clothes off. Only a fraction of them have the desire. Judging from the evidence, there aren't enough, at the wages of elementary school teachers or administrative assistants. In order to persuade more women to accept this form of employment, they need to be paid more.
The more technical answer is that every job function has, at any moment, a certain number of positions. In order to fill all of them, you only have to pay enough to hire the last person hired. Why? Because if any one person already working at that job quits, then the person they hire to fill their job will probably take the job for the same amount of money as the last person hired. Or close enough. Now, obviously, experienced workers get paid more, but not an awful lot more.