My own reason to prefer monogamy is that I’d like to be by far the most important person to my partner (other than themselves) in the same way that they would be the most important person to me. Polyamory would make the boundary between “us” and the rest of the world a bit less sharp and that doesn’t seem worth the benefits (the first reason also applies to me, the benefits don’t seem that great).
My own reason to prefer monogamy is that I’d like to be by far the most important person to my partner (other than themselves) in the same way that they would be the most important person to me. Polyamory would make the boundary between “us” and the rest of the world a bit less sharp and that doesn’t seem worth the benefits (the first reason also applies to me, the benefits don’t seem that great).