A question for my Poly friends

I know quite a few people who live a poly lifestyle, those who do it successfully seem to have to put an inordinately huge amount of hard work in. Personally I find working on a single relationship to be challenging enough (and yes I did give the alternative a try a long time ago) and I'm finding it hard to wrap my brain around why a person would choose to so exponentially complicate their love life. I have seen so much heartache and disapointment and what I can't help but consider some extremely unhealthy situations.

Please understand that I don't disaprove of a poly lifestyle on principle, my orderly German Capricorn brain just boggles at the resulting complications.