Why do men want to have threesomes?

Threesome is the favorite kink for Americans. Why it is so welcomed by many people? Imagine the pleasure of having sex with your partner, double it for a threesome. Besides, threesome fulfills the fantasy of most men have about wife-sharing. It is kind of kinky lifestyle watching someone having sex with their wife. It makes them angry but also turns them on. Someone even want their wife more when watching their wife being taken by another men. Many swinger couples and singles share the same idea.