Polyamory doesn't work because people will always have a sliver of jealousy in them. Individuals will always play favorites, snubbed people will always be frustrated, and any polyamorous group will always crumble and fall apart into pairs.
You know your group of friends from high school? That gaggle of ten or so fuckers you hung out with? You know how there was always one or two good looking people, a bunch of average cunts, and then two or three ugly stupid fuckers nobody really liked but put up with because they at least didn't try to fuck anybody?
Yeah. Try to throw in a mutual "everybody fucks everybody" condition, see how that works out.
Bonus points if the group lasts longer than a week before the beautiful people ditch you, or try to kick out the ugly ones and cause a shitstorm.
Polyamory is a pipe dream. Ugly people think it will let them get some, which it won't, and beautiful people, or at least unfaithful whores, think it's their ticket to an easy harem. Everyone loves the idea of sleeping with several different people but nobody considers the sharing part, or the "being shared" part.