Polygamy is most common is places where women don’t have civil rights. When women can get an education, hold a job, own property and vote, they don’t choose to go into polygamy.
Economies of polygamous countries are effected negatively when there are a lot of men without wives and families and when women are restricted in how they can contribute to the economy.
Polygamy is part of the reason the countries that allow it are usually poor. The only ones with real money are those who have oil revenue from the free democratic countries that don’t allow polygamy.