I think there are an unfortunate number of monogamous people who decide to try polyamory to fix or hold on to a dying relationship. It’s not a surprise that that often goes extremely poorly. It’s not for everyone and it’s not gonna fix any problems.
I’ve dated a couple of people who are poly, and while I’d always been in monogamous relationships, I was open to the idea. I don’t think love is a finite resource, and I’m not a jealous person at all, and it turns out, it doesn’t bother me at all. I also stay well away from anyone who thrives on drama, so all involved were very honest and adult about the whole thing. I wasn’t in a good headspace for any relationship at the time, so it didn’t work, but I’d absolutely be willing to try it again.