Taking a thought from Lynn's post- most people desire close friendship relationships with a group of people rather than just one person. If someone can have poly-platonic feelings, why should a person not feel romantic connections with more than one person? Whether someone is of loose morals or whatever is a personality trait or behavioural trait. There is no reason why a person should not feel they want to surround themselves with a different kind of love and, as others have said, polyamory is as much a part of nature as monogamy, just some species have different survival tactics to others.