That's because Australia, like many countries across Europe and Latin America, has a "notice and takedown" regime in its "intermediary liability" laws, which means that social media platforms, service providers, and other internet services that enable people to upload and share content online may become liable for their users' content as soon as they are notified that it may be defamatory.
You may ask why, of all the worthy causes in the world, is intermediary liability - something that sounds so intensely boring - so critically important? The answer is that the internet is now the arena for almost all important social, political, and cultural debates. If we're not allowed to even acknowledge certain problems online, we can't ever start to change them.