HughRistik:

I'm not sure of Vladimir's reasoning, but I might speculate that men at the top tiers of attractiveness don't even need to join the poly community to have multiple partners.

Furthermore, being poly may have certain correlates (e.g. geekiness) that are only attractive to subsets of the female population (e.g. the subset that is poly).

Yes, that's pretty much what I had in mind. For a man of very high attractiveness, becoming a card-carrying polyamorist is a deal that brings no real benefit for the cost. Such men already have a rich array of options in which they'll have the upper hand, including polygynous arrangements.