Robert Trivers (I believe) isolated the common denominator of sexual dimorphism as
minimal investment in offspring, which is harmonious with much observation of the living world. Polyandry is definately the exception to the rule. I'm not posting with an answer, just curiosity.
Natural selection is a
predictive theory, not just an explanatory one. If polyandry is observed, you can bet there's a benefit for it...even if it's not immediately obvious to us. I'm surprised more knowledgeable members of this forum havn't engaged this thread.
