Just because the Bible records something, doesn't mean that it approves it. Right from the beginning of scripture in Genesis chapter 2 it says:
24 Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh.
Not only that, in Deuteronomy chapter 17 it states:
17 Neither shall he multiply wives for himself, lest his heart turn away; nor shall he greatly multiply silver and gold for himself.
We know that polygamous relationships cause problems for Solomon, David, and others. In addition we have qualifications for elders in 1 Timothy 3:
2 A bishop then must be blameless, the husband of one wife, temperate, sober-minded, of good behavior, hospitable, able to teach;
Kings in the old testament and church leaders in the new testament are the role models for the moral community. What went for the king and the church leader was to apply to the people. Just because it is not judged on the spot in the old testament does not mean that it will not be accounted for in time. We will all have to account for our actions.
Finally, the fact that God still blessed people like Abraham, Jacob, David, and Solomon, even though they had polygamous relationships, it shows that we serve a God of grace. He will still work through these characters in scripture to achieve his overall will.