Big Love and Polygamy

I am a huge fan of the HBO show "Big Love". I love the complexities of multi-marriages and all the hoopla as they try and keep it a secret, while concurrently trying to mainstream it.
That said-I have strong opinion of Polygamy . . . I am all for it! BUT AND THE BUT IS BIG: no children are to be born from these unions. Why should children be brought into this mess. And I don't care what those women who don't mind sharing their man and having a once or twice a week booty-call say . . . . this isn't good for kids! I also think that the women should be no younger than 21 to get married. Anyone below that age isn't mature enough to make such a monumental commitment.
I have a question, Why would any woman want to do this? I understand that for the man this is Utopia, but for the woman WHY?