Even though some ancient followers of God had multiple wives, it was never God's intention from the beginning.
Jacob had multiple wives, but they fought each other for Jacob's love.
Solomon had multiple wives, but they led him away from God.
God's intention was one man and one woman from the beginning when God created them:
"For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one flesh." (Genesis 2:24)
A man and woman become one flesh. But a man and several woman is not God's will.
God allowed this during ancient times, because people wanted to be like the other nations (which allowed polygamy at the time) and because of their hardness of heart.
But when Jesus came, He defined what marriage is once again.
"They said, 'Moses permitted a man to write a certificate of divorce and send her away.' But Jesus said to them, 'Because of your hardness of heart he wrote you this commandment. But from the beginning of creation, God made them male and female. For this reason a man shall leave his father and mother, and the two shall become one flesh; so they are no longer two, but one flesh. What therefore God has joined together, let no man separate.'" (Mark 10:4-9)
So Jesus forbid divorce in general and He defined marriage as one man and one woman, saying they are no longer two people but one flesh.
Do you think God favors polygamy (which defies His intention of joining one man and one woman together)?