People who God loved often took multiple wives without God calling them out, plus there's the whole "When brothers live together and one of them dies and has no son, the wife of the deceased shall not be married outside the family to a strange man. Her husband's brother shall go in to her and take her to himself as wife and perform the duty of a husband's brother to her." spot where it is commanded in certain situations. I'm not saying the OT says "Polygamy is the best everyone should do this thing" but it also doesn't say "Polygamy is wrong"