Because there is no systemic pattern of cops killing Australian women, over and over and over and over again and not being charged at all. The police officer responsible was immediately fired and charged with murder, of which he was convicted [0]. Justice was served, what would people protest for?
Compare that to Floyd, where it took sustained protests to get the main perpetrator arrested.
When something terrible happens once, it is sad. When it happens over and over again, its not "bad apples" but a systemic problem that needs to be fixed. The protests are about similar incidents (cops killing black Americans) happening throughout the country. The people who protest see that reality and are moved enough to get out there and do something, anything in the face of that injustice.
The basic governing principles of the criminal justice system in the US is that the punishment should fit the crime. Regardless of however flawed human being George Floyd was, he did not deserve to die as he did. Many, many Black Americans did not deserve to die.
Please educate yourself if you're genuinely interested in learning about the reason why so much of the country feels the need to come out and protest during a deadly pandemic.
[0]: https://en.wikipedia.org/wiki/Shooting_of_Justine_Damond#Tri...