The finches on the Galápagos Islands more closely resemble the finches on the nearby continent of South America than the finches on the island of New Guinea off the coast of Australia. What is the reason for this?

I believe the reason for this would be geographical evolution. Different ecosystems cause the finches to evolve differently over time. Also, since the finches on the Galápagos Islands are closer to the one in South America, it is likely that finches from there (South America) could have moved to the islands, contributing to the evolutionary process.