Although it may be counter-intuitive, monogamy benefits men more than it does women. Sure, women aren't treated like chattel, but in polygamous powerful men have the harems, the rich men have many wives, and the majority of men have nothing. Monogamy evened the playing field and allowed one woman for every man.
I think this article is a good example of the theory. As the Chinese become more affluent, it's no surprise that the men who can afford it have mistress issues while, as kimmy said, millions of men are without wives.