If slavery and multiple wives were allowed in the Old Testament, I guess we could say they were a reflection of the times. But then some people are using this same reasoning to say that homosexuality is merely a reflection of our times… why was slavery and multiple wives okay back then, but then now it is not - and maybe homosexuality wasn’t okay back then, but now it is? I totally don’t believe any of this, but anticipate questions from others similar to this one…
What God allows is up to God. It is not our decision to make. The people who are aguing that homesexual activities is ok now based on examples you used could also justify murder and stealing. But we know that it isn’t the case.
God led the Israelites into greater degrees of holiness, which entailed cutting out activities that were not up to God’s standard. So, they were restricted from at first having several wives to just one. Slavery doesn’t belong in this question, however. Slavery back then was only to repay a debt, not the racial slavery we are familiar with now.
So, following the model of restricting activities, it doesn’t make sense that an activity that was banned (and for good reason!) would later become allowed.
There is nothing in the Old Testatment that says that multiple wives or homosexual behaviour is “ok”.
There are many examples of mutiple wives - but never expressly condoned by God and each instance of multiple wives (if you sort through the stories) inevitably led to strife and conflict.
To the contrary, there are verses in the Old Testatment specifically urging the Jewish people to remain with the woman of their youth (e.g., their wife) and forbidding divorse or adultery. Proverbs, in particular, includes many verses to this effect.
There are some who have read “polgyamy” into these old testatemnet verses as somehow an explicitly permitted, or even, recommended practice. That is a perversion of the scriptures, I believe.