I don't think anyone's ignoring it, you have to consider everything that has been said about marriage.
Mark 10:6-9
"But at the beginning of creation God 'made them male and female.' 'For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh.' So they are no longer two, but one. Therefore what God has joined together, let man not separate."
Proverbs 19:14
" House and riches are the inheritance of fathers: and a prudent wife is from the LORD.'
2 Samuel 12:8
"And I gave thee thy master's house, and thy master's wives into thy bosom, and gave thee the house of Israel and of Judah; and if that had been too little, I would moreover have given unto thee such and such things."
So when people marry, God has joined them together....let no man separate them. A prudent wife is from the Lord, and God has personally given men more than one wife. Sooo.....how can it be said that having more than one wife is sinful if God has joined them together? Soooo, all of a sudden, it's a sin out of the blue when it wasn't before? If you want to speak of the ideal, "Ideally" one should not marry at all.
1 Corinthians 7:8
" Now to the unmarried and the widows I say: It is good for them to stay unmarried, as I am."