Some people seem to be having wonderful polyamorous relationships while other seems to suffer in terrible relationships where they insists on being polyamorous.
For me this seems unrelated to polyamory. It seems more to be the case that the people who are emotionally stable have good relationships and the people who are unstable struggle to form good relationships.
At the same time it seems that polyamory might be appealing to many who can't make "normal" relationships work. So my guess would be there are two distinct groups who are drawn to polyamory.
Highly emotionally intelligent people who communicate their needs and function well within relationships who wants more relationships and people who struggle with relationships who sees polyamory as the solution and monogamy as the reason for their previous problems in relationships.