140 countries practice polygamy to one extent or another. And, polygamists tend to live longer than monogamists (unless your wife kills you). Scientists are trying to find out. Why not. They don't have anything better to do.
Of course, almost all of this polygamy is one man married to many women. Why are there no societies where one woman is married to many men? The Little Woman says it is because no one woman can pick up that many socks.