>People living in southeast Asia 70,000 years ago were certainly sailing out of sight of land, because they reached and colonized Australia. It beggars belief to suggest they did not also go to other places in equally easy reach, and then others from there.
My understanding is that those who reached Australia did not go further, because they forgot how to build ocean-worthy vessels.
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.
My understanding is that those who reached Australia did not go further, because they forgot how to build ocean-worthy vessels.