I don’t think Deut 17:14-17 prohibits polygamy. It comes right after a similarly worded passage regarding horses, which I assume doesn’t mean that one can’t have two horses. I think what it says is that one shouldn’t greedily accumulate women as with horses and gold.
Prohibitions on polygamy start with the New Testament.
The Romans took marriage rather lightly. Homosexuality was hardly unknown to them. The Greeks celebrated homosexuality and often cared about their boyfriends as much or more than their wives, whose purpose was in many cases solely procreational.
The collapse of both the Greek and Roman empires occurred after their acceptance of homosexuality in their midst. The devestating impacts of homosexuality in our society are soon being felt.