In the case of Aboriginal title they have to show that they still have a connection to the land, i.e, go there regularly to hunt/gather or for religious ceremonies etc. So you can get competing claims because one tribe used the land, but then were pushed out by another tribe and they're both making claims to the land, so the court has to decide which group gets the title.

It's also not straightforward because often there are many different groups that claim the same piece of land. Or where they can't decide the boundaries between the different mobs lands. I believe they also have to show that they have a continuing connection to the land and not just "my great great great grandfather lived here".

Also title to the land doesn't necessarily mean they own the land it just means mining companies and local government have to negotiate with them, and possibly provide compensation for the use of the land. But very often they can't just block mining companies from mining the land all together.