I don't know why this is surprising. All ancient cultures practiced polygamy and all ancient kings had harems. Monogamy is solely an invention of the Church and of Christianity (along with banning homosexuality, incest and infanticide). Where ever Christianity took hold it was able to eliminate polygamy by 3rd and 4th generation (Of course there were still socially stigmatized relationships like mistresses and affairs but they were considered sinful and had no social sanction).

Feminists hate the Church, but the the biggest social advancement of women is owed in fact to the Church. Feminists hate that Christ forbid divorce, but in fact that teaching helped millions of women. Of course this was not without dividends for the western civilization as a whole. Idea of one woman for one man elevated the status of women and made western civilization way more productive that the others because women now had more status and contributed more.