I don't think there were relatively unlimited resources, many islands were quite heavily settled. Tupaia, for instance, was born on Ra'iatea but had to flee to Tahiti due to conflict. He then went with the Cook expedition and taught them about Polynesian navigation.

It's very possible that some of the longest distance voyages such as the ones that found the corners of the Polynesian triangle in NZ, Easter Island, and Hawaii were triggered by conflicts with the losing group opting to go on an exploratory voyage.