The same reason it happens everywhere: Men get away with it. Westerners are not some different species, you know. If you allow them to beat women with no repercussions, they will do it, just as if there were no repercussions to beating a man.
How they get away with it, would be the more interesting question. I think the trick is conservative gender roles. You need to shame/force the woman into becoming a breeder and thus make her dependent upon the male. Make her not have an education (college is for filthy sluts!) and as little work experience as possible by marrying early. Basically have her stay home and raise kids all day. You also need to indoctrinate her into considering the traditional family sacred and inviolable (legislation helps) so that she will stay because Jesus said so or "for the good of the children". Then, even if you beat her, her options are drastically limited, thus minimizing the consequences.