The problem is that they’re talking about Christian churches, where polygamy has never been okay. And even Jews abandoned polygamy as they grew into God’s law.
Polygamy is a very primitive pre-Revelation social structure in which a powerful man gets to collect a herd of women. As societies, under the influence of Christianity, move towards an appreciation of the individual and the dignity of women, polygamy disappears. It’s not compatible with Christianity.
Turkson (who seems to be in favor of divorce and remarriage) is famous for his “Africans are different” nonsense. Africans are human beings like all the rest of us and are called to live in Christ just as the rest of us are. They have to learn it, and that’s what missionaries and solid teachings are for.
Polygamy is still accepted in Judaism, just rarely practiced. If you want the citation, I’ll find it.