Because territorialism is ubiquitous in the animal kingdom and aboriginal societies also had a concept of territory. They reject it because its a social convention and therefore its always possible to reject it. But they reject it because they don’t like being excluded from territories and they think rejecting the social convention of land ownership will result in a new arrangement where they are no longer excluded from territories. However this is like rejecting the social convention of English because you want to be able to make noises that English-speakers consider to be insulting. They haven’t addressed the fact that society relies on ownership notions in order to do things like produce food and housing; and they have no plan to allocate scarce resources in the absence of ownership norms.

> I've always interpreted this as being an attempt to call attention to things like the relative shortness of our lives in comparison to the earth and an argument that there's a certain amount of hubris involved in saying that you own components of ecosystems that you exist within and depend on to live.

Thats a valid response to a metaphysical concept of ownership as a thing-in-itself that has meaning outside of human relations. My response is to ground ownership in reciprocal norms that arise emergently from human interaction. And to justify them on the basis of egalitarian human rights.