I suspect that Jomo Mojo has the answer. Monogamy tended to be the more prevalent practice among the Europeans–the Greeks and Romans enshrined the practice in their laws, the Celts and Germanic tribes appear to have practiced a form of polygyny in concubinage, but only among the wealthiest nobles–while polygny was more common among the Asian and African groups. At the time Christianity broke out of Judaism into the Gentile Roman world, even the areas of Africa and Asia into which it first spread were dominated by Roman law (which did not tend to suppress local customs, but would have influenced thoughts on the subject).
Judaism, arising in Asia, has no proscription against polygyny, and the practice continued in Europe for many years. However, the Roman-influenced social mores continued to provide a certain pressure to limit the number of people who practiced polygyny. When polygyny was practiced, from time to time, it had the result of irritating the Christian neighbors of those who practiced it. In 950, in central Europe, a synod called by Rabbi Gershom of Mainz declared that Jews in that region should adhere to monogamy for 400 years. Rabbi Gershom’s reputation for wisdom was so great, that all the Jews of Europe adopted the practice and, by 1350, the practice was so ingrained that they continued it without any serious effort to review the “law.”
Jews in the Middle East, living among polygynous Muslims, continued to practice polygyny into the 20th century. However, polygyny requires a certain amount of wealth to succeed, and it has never been a prevalent practice even where it is allowed.
Christian thought was directly influenced by Roman law, but was also influenced by Scripture. While there is no prohibition against polgyny, all the examples of marriage that are raised in the New Testament describe monogamous relationships. Even the story (Mt 22, Mk 6, Lk 22) of the woman who married seven brothers, serially, in compliance with the levirate law, implies monogamy (or, at least, a shunning of polyandry), in its question of who shall be her husband after the resurrection.
I would tend to see the admonition that a bishop be a “man of one wife” would reinforce monogamy, but not that the idea arose there.