That’s a question you can take up with the framers of the Constitution. Their wording of the delegation of the deportation power is what caused it.

A person born overseas to two Australian parents is also impossible to deport because they’re an Australian Citizen, who by definition is not an alien. The same applies to a person of an Aboriginal bloodline because they cannot be alien either because they were in Australia first and the the colonial government doesn’t really have the right to tell the Aboriginal people that a person two generations removed isn’t Aboriginal.

It’s not a privilege they have, it’s an inalienable right.