Why do discussions about polygamy always centre around sex? It seems such a short sighted view. A man who marries a number of wives has to provide for them all and their offspring, deal with their jealous infighting, etc .. hardly the image of a constant orgy.
The idea that a man with multiple wives must provide for them is not universal to polygynists. Some of them really do treat it like an ongoing adolescent fantasy, and the women (and girls) are often coerced by means of living in an isolated "community". "Excess" young men are expelled.