The fact we haven't discovered clear evidence yet is not at all surprising. Even the evidence of Aboriginal settlement that far back is very, very limited. It

The fact we haven't discovered clear evidence yet is not at all surprising. Even the evidence of Aboriginal settlement that far back is very, very limited. It also of course depends on what you mean buy "we"; given the presence of other ancient hominids we could interbreed with in the region, it's not impossible others were there first by many millennia with nothing to show for it. We've got to keep in mind how incredible sparse the archeological record is for anything that far back - we didn't know a single thing about the existence of Homo floresiensis (itself very, very close to the ancient Sahul continent) and still wouldn't if it weren't for the discovery of a single site in 2003. Unfortunately, the importance of accepting the Aboriginals as "first" has likely politicized the science here and is so important as a fundamental tenet of some political claims that it will tinge future evidence one way or another.