Going to get downvoted but who cares it's just Internet points.

Honestly for me I just don't really care for aboriginal mythology. It has no connection to my history or the events that shaped the world. There is very little recorded history of any native people who did not have a written language. This means that they have a lot of mythologies created about the same concepts as others (birth, life, death, animals or weather conditions) but little history of their people. There are no markers for the "great" (important to historical events) person of history was born or the trail they blazed through life. I don't have a written account of why a king choose to build an empire in Australia or if there ever was such a thing. I can read a translation of ceasers book with context provided by his contemporary authors. People are infatuated with the lives of powerful individuals. In a similar fashion people are interested in the most advanced/powerful Kingdoms of old. Now what I say here is shit but I am leading up to it. The cultures you mention are not important to the course of history and will die out in time because they add little to the overall tapestry of the human condition.

We will, as the world grows more homogeneous, remember the moves and shakers history. The dominant powers of old more than we will remember the conquered short lived societies that surrounded then. Most people know of Muhammad Ali but do we know who he bested to become the greatest? Some do most don't because we aren't as interested in the small people of history only the giants. Is it a loss that less is remembered of the smaller cultures maybe but in the end we have one life and only so many hours in a day to learn. It is good that you have an interest in these cultures but for most of us our lives are to busy to focus on all the things we like.

For me they just don't interest me when compared to Greece, Rome, Arabia, China, Britain or America. I have no connection to the stories therefore they have little importance to me. Do I fret about this? No, because I have so little time on my plate for the things I enjoy that I don't have time to consider or care about the things that have no effect on me. In the end this is my speculation about why less smaller cultures are investigated by us so take it for what it is.