its based on his level of sexual desire some men have more and need multiple wives or risk facing zina and the temptations of shaytan, its not just about allowed its a must if you have that high of a level of temptations to go the halal route and preventing shaytans angle of opportunity of adultery, which is why he's inflicting women with whispers of jealousy so they don't allow there husband the halal(4 wives) and lead him susceptible to the haram and vile women like
@Knowles who would go through with making him adulteress like she's planning with this professor