What is up with the fact that like 95% of people in "polyamorous" relationships have a very identifiable set of phenotypes? A lot of them are pudgy, low muscle

What is up with the fact that like 95% of people in "polyamorous" relationships have a very identifiable set of phenotypes? A lot of them are pudgy, low muscle mass, pasty, etc. Not trying to throw shade - legitimately curious why they all seem to fit into this category. It's not clear to me if polyamory allows them easier access to sex than monogamy or something - it certainly does't seem to get them access to partners that would be out-of-reach otherwise, as most polyamorous groups seem to be within a relatively similar attractiveness band.