Exactly. I think a lot of people bring their mono/nuclear family/breeder ideas over to the poly world and want to impose them. That's fine if that's what you and yours want for your relationship, but not everyone wants to just keep expanding their family group. Some people want to keep metamours separate and enjoy different relationships with different people.
Obviously the Hinge has to live up to promises made to both/all sides, but when one meta begins dictating the relationship of the other, there's a problem.
Me - male, 42, poly, straight, in a serious relationship with Audrey, also casually dating.
Audrey - female, 20, poly, pansexual, also casually dating.