Why the hell people like poly so much?
Because it's different, also allows for multiple "best boy/girl" to win. It solves a lot of the drama that occurs in romcoms. It takes a bit more effort and commitment to make it work, but monogamy is also something you have to make work for a happy relationship.
Then there's how we can see IRL that monogamy for the sake of monogamy can lead to conflict, cheating being the prime (but not sole) example. Not everyone will be open/poly, but forcing people who can and do harbor feelings for multiple people into that mindset because it's "the correct way", via social norms and/or taboos, will cause strife somewhere along the line. It's still considered "odd/weird" by the masses when people encounter open relationships, and not because it's not natural but because we've been conditioned to view them that way.
To conclude, neither poly nor mono are the correct way, they both are natural. But one of them gets passed over in media because of norms which makes those that make it through the cracks celebrated.