Islam allows men to have up to 4 wives (simultaneously). Why would an overwhelmingly Muslim country, such as Turkey or Tunisia, ban polygamy?
Not banning it would of course not prevent most people to live as regular monogamous couple.
In order to be clear (seeing the comments I see the confusion): I know already that polygamy in 2017 is rare even in countries that allow it, and that there is many reasons for being against this lifestyle. Yet, I am not asking why don't anybody wants to have multiple wives / share their husbands with other wives. I am merely asking why a muslim country would make polygamy a criminal offense.