Maybe I'm being judgemental, but I've never, ever heard of anyone in a polyamorous relationship where it wasn't a seriously exploitative tactic on the part of the person proposing it. The
Bex thread is a good example too.
You read the occasional article in the newspaper where some sadsack journo forces a smile on his face and writes the required "woke" article about how he and his wife are in an open relationship and he's fine with it.... Except he's not really exercising the freedom, he really doesn't like to hear about his wife's other partners, he's definitely uncomfortable if they ever meet and it makes things awkward with regards having sex with her himself... in fact they've mostly stopped having sex. But it's fine, you guys, it's a great lifestyle!
Then they split up about 1-2 years later after having dragged the relationship on long past the point where they should have divorced already. Maybe there are some people it works for, but I think they must be keeping it to themselves.