There was nowhere further to go, unless you count New Zealand. We don't know if they reached New Zealand. But Australia/New Guinea/Tasmania (called Sahul) was p

There was nowhere further to go, unless you count New Zealand. We don't know if they reached New Zealand. But Australia/New Guinea/Tasmania (called Sahul) was plenty of territory, by itself. The people who sailed to Australia were of a culture that could sail in any direction, and would have. You would need to come up with a reason for them not to.