Adam was the first man. He was monogamous-- so monogamy is the ideal.
Cain was the first person with two wives. He was cursed-- he wasn’t the best role model.
Noah had one wife. Each of his sons had one wife.
Abraham had one wife, until Sarah persuaded him to take a concubine. We all know how that worked out for them…
Isaac had one wife.
Jacob wanted one wife, but was tricked into taking two. And then each of his wives had him take their slaves as concubines. And we all know how happy that family was…
Jacob, Moses, and Aaron were all monogamous, as far as we can tell.
By the time you get to the Judges and the Kings of Israel, polygamy has really picked up steam. But amongst the Hebrews, polygamy was associated with paganism and pagan influences. So while even modern Jews have rules of conduct in countries that allow for polygamy, and while Jewish people have been polygamous at various points in time in various places, it’s still something that’s discouraged… because it strays from that original ideal.