and part of the reason why they do that is that they themselves want exclusivity from their partners, otherwise they'd just be in open relationship
Exactly.
They could be polygamous all they wanted ... There's a community.
They don't want to be polygamous, they want all the benefits of monogamy for themselves while not tolerating the disadvantages and sacrifices of monogamy for them.
Most men I know who are cheaters and sleazes are possessive of their partners and have massive double standards for them. My mum has three sisters and the only two who don't socialise alone - because they are heavily "discouraged" from socialising alone, have cheating, sleazy, sex industry using husbands. And they are double standarded, jealous, posessive, controlling men.
Look at what men with ultimate power in past times did - kept hundreds of women in harems , fucked their way through them and produced hundreds of kids with them; while it was punishable by death if the women interacted with another man. They even castrated their guards and used guards of different races so it would be obvious if they'd had sex and fathered any kids in the harem.
That's what these men are a low income, Jeremy Kyle version of.
They don't want polygamy.
Cheating is not because monogamy is forced on them. They want & choose monogamy, just a fake, one sided, manipulative version of it where they sacrifice nothing to get what they want from their partners.