Judging from how many nominally monogamous people switched to being nominally polygamous in my social circle as the social norm changed, versus how many didn't, I strongly doubt that a plurality of the population is sufficiently exclusively and innately monogamous that considering alternatives is a waste of time.

Then again, I also doubt that 95% of the population is exclusively and innately heterosexual. OTOH, I've never lived in a normatively bisexual community, so I have minimal data