This is a question that has multiple answers.
I will give you the Top 10 reasons why men go for a second wife from personal experience and assessment, in their descending order.
LUST AND IMMATURITY- A man will marry as many women as the size of his LUST. The apostle Paul instructed us to marry ONE woman to satisfy our LUST. However, there are men whose hearts were filled with too much LUST and broke the banks of their hearts. A Mature man must be able to control his LUST. When we were boys we would play around with girls like entertainment objects. When we become MEN; fathers; husbands; sons-in-law we must mature up and live decently, honourably and Godly.
DISRESPECTFUL 1st WIFE: No man can ever stand an abusive, disobedient, noisy and unthankful wife. Every man wants a dove in his wife and not hornbills and weaver birds that abuse and insult and nag and click and openly fails to honour and respect him.
LACK OF SELF-RESPECT AND PERSONAL CORE VALUES: If a man respects himself and has faithfulness, Trust and Respect for others as his Core Values, he will see it DIRTY moving his manhood from one wife to the other. He will sympathize with his wife and always seek to respect her as she respects him. He will want to raise a biblically grounded family. A man who lacks self-respect doesn’t care what he does with his life or with the life of his children or his wife. He lives by his ego and his ‘big’ head full of foolish traditional dogmas.
MONEY WITHOUT ETHOS: A man who gets money abruptly may start revealing weird characters. Some become alcoholics; some womanizers and yet some oppressors of others. Most Men bring in a 2nd wife upon getting a promotion; a well-paying job; a SportPesa jackpot or Tea/Sugarcane/Coffee boom. When a man who has never had a million eventually gets one; his mind might migrate to WOMEN; ALCOHOL; POLITICS or all the three.
FAMILY: If the family feels like their son has been colonized by the wife, they will push their son into getting someone who is ready to welcome and support them. If the 1st wife is going to keep her husband and his money in her wallet, pushing the husband to send all his money to her parents yet she feels bad when her husband is helping his family, believe me a more hospitable and pro-husband family wife will be in not longer. The 1st wives must be ready to integrate into the husband’s family.
PEER PRESSURE: There is more Peer Pressure among married men than their children. Just look at the responses under this post. If you sit with 10 polygamous men who ridicule and mock you of being ONE-EYED, believe me you, however grounded in Scripture you might be, bad company corrupts Good morals.
PRODUCTIVITY: This is both biological and economical. You want a woman who shares your vision and supports you to invest and raise your children in a better way. You don’t want a wasteful person who brings nothing on the table. If a man notices that the wife he has is going to waste their little resources and make life hard, he may opt to find a woman with a vision. The biological side is 3 pointed: a) a wife that is not delivering BOYS(which is stupid as it is a man who gives the Y-chromosome). b) a wife that is barren by circumstances(which needs mutual consent) c) a wife who goes for Family Planning secretly without informing the husband.
ABSENTEE WIVES: Have you met those wives who are married to their jobs and bosses and are travelling 25 days a month and spending the remaining 5 days in board meetings and workshops?
DENIAL OR MEASUREMENT OF INTIMACY: Those wives who mark their calendar and say,”We did it on 24th August, it is not even a month since we did it last. Am I chicken or a dog?” That one is sending her husband straight into the hands of a woman that will receive him with both open hands and legs.
FAILURE TO BE DEEPLY SOAKED IN THE WORD OF GOD: Scripture regulates human behavior; Scripture gives wisdom on things marriage. Scripture counsels and guides.
Men that fall away from Marriage by God’s design are men who are not firmly grounded in the word of God.
They live by their own wisdom, traditional misconceptions, family routine and beliefs and peer advice