In a poly I would guess people need to feel attached to a group not a single individual, in a sense loving all people in the group almost equally. Mostly, we are not raised that way and culturally it would be unconventional, to say the least.

Loving people equally is impossible. Even poly people have a 'primary' introducing hierarchy and preference.

A group of people sleeping together is not a stable community. It's filled with people who are trying to sleep with other people inside and outside of the group who are vocal about being able to spend time, money, and effort on others for sex. There's nothing binding a group like this together besides sex.

Even normal community activities like volunteering or sports clubs have drama and people who end up hating each other. Add sex in the mix and you've created an explosive dynamic.