as salam alaikum
it is not difficult for all men to convince their wives to have another wife and it is not difficult for all wives to accept an husband with more than one wife. Also, it is not necessary for all men to have more than one wife and in many cases it may be detrimental for them. People differs and sometimes there are situations that call for specific choices. For example the Qur'an says: "And if you fear that you will not be able to to justice to the orphan girls, then marry of women as may be agreeable to you two or three or four, but if you fear that you will not be able to deal equitably then one" (4:3).
With prayers for your success.