(Some) economists, every now and then, look for reasons why polygamy cannot be efficient. How about this?:
Over the last six years, hundreds of teenage boys have been expelled
or felt compelled to leave the polygamous settlement that straddles
Colorado City, Ariz., and Hildale, Utah.
usually the reason given for expulsion, but former sect members and
state legal officials say the exodus of males – the expulsion of girls
is rarer – also remedies a huge imbalance in the marriage market.
Members of the sect believe that to reach eternal salvation, men are
supposed to have at least three wives.
Here is the longer article, which has several interesting parts.