The way this question is phrased is bizarre, but I'm going to try to answer you in good faith knowing that might be a trap.
In general, most societies and cultures are set up around monogamous partnerships, so people are born into those roles and expectations. People may learn as they grow up that they prefer polyamory, but that doesn't make it like 'correct' for everyone. I know polyamory isn't for me personally because I don't like people generally and need devotion from my partner and a poly relationship would get in the way of that for me. Cheating happens in polyamorous relationships too, so if you're looking at polyamory as a solution for being unfaithful, you're probably going to be disappointed. I think looking at people having sexual relationships throughout their lives as trying to 'collect' sexual partners is a really immature way of seeing people. People fuck. Sometimes people fuck one person their whole lives, some people fuck a bunch of different people through their lives. That doesn't have any effect on whether they prefer monogamy or polyamory, it's just what people do. If you yourself like polyamory, that's awesome! Your experiences are not universal. Sex in advertisements is designed to manipulate base emotions because those emotions work on large swaths of people, it's not indicative of society's attitude or even awareness of monogamy. People are gooning because capitalism took all the third spaces and only left the internet to replace it. Gooning is one of the few things people can do for free now. If you own a phone or a laptop, you have the ability to goon. You're statistically unlikely to be near a mall or a recreation center or somewhere else you can spend time without having to spend money. If you're in America, you're statistically in a food desert. So people are going to goon and thirst over the things they see in their little internet box, which is again completely unrelated to monogamy or polyamory.
I hope this was a useful explanation for someone.