The most obvious one: People age.
I really believe people that leave due to their partners appearance because of childbirth and the like aren’t fit for marriage. At the end of the day, you can work with your wife to get into shape. But what happens when she becomes wrinkly and now has saggy skin? What happens when their wife reaches 47+ and has now hit menopause?
These are the ones that trade their wives in for a new version, they don't see women as human beings. They marry a woman when she's beautiful and young, when they drain her of her life force, they get another wife and repeat the process.
I remember someone posted a thread about a man that bragged about being married a shocking number of times. Waa kuwaas oo kale. I struggle to believe they're headed to heaven walahi.