Yeah, I just think the poly relationship has more places where things can go wrong. In a monogamous one, you need to two people who like each other and are compatible. In a poly, even with only 3 people, you need A and B to be compatible, A and C, and C and B. Adding one extra person into the mix complicates the relationship 3-fold depending on the nature of those relationships. They don’t all have to be in a relationship with one another, but you’re still adding more avenues for drama and collapse in one relationship, not to mention how one relationship could impact the other. If A is having drama with C, the frustration of that failing connection could also impact their relationship with B. I think it’s easier to fail not by any sort of moral failing of polyamorous people, only that the nature of those relationships is inherently less stable through its myriad of moving parts
But there is for sure an element of bias, where heteronormativity gets a pass for being the standard