The reason for this is both nations closed the borders early back in February. When that happened the fuckwit Tedros Adhanom Ghebreyesus, director-general of the World Health Organization came on national TV of Australia and said "There's no reason to restrict travel". This was in February. Listen to the fuckwit say it here: https://www.abc.net.au/radio/programs/pm/is-closing-borders-... Lawrence Gostin, an official in WHO is also quoted in the above "it is unlawful, unnecessary and in breach of international law".
I normally wouldn't be so harsh on criticism but this was in February. The border closure wasn't some racist Donald Trump style effort. It was two countries doing the right thing but the WHO is so corrupt and fucked up they tried to stop it, even threatening they'd bring the border closures to the international courts.