One of those clauses that makes little sense upon examination. They created the problem and it's theirs, not the country they betrayed. Australia owes them nothing. To say otherwise is like saying you owe cancer cells a new liveable situation when you drive them out of your body with chemo.
It is probably for compliance with the UN convention on statelessness. The US is not a party to that but Australia is. Their postwar era politicians no doubt failed to anticipate problems like future politicians deliberately admitting hundreds of thousands of moslems to terrorize the community, while taking advantage of laws intended to protect legitimate war refugees to shield themselves from consequences.