Actually, polygamy in Islam was never about maintaining an equal ratio of women and men. The exact reasoning is unknown and left to the infinite wisdom of God. What polygamy in Islam does is help those men who have a desire to take on multiple wives and want to have larger families. Subject to them meeting the criteria set by Allah of equal treatment between his wives. This allowance for men is also considered a form of social care for certain women who otherwise would be marginalized or sidelined. Such as widows, divorcees who may have children already, women over a certain age, women who may some sort of disability etc.