It is mandatory in many countries, not just Australia. Europe, Japan, Brazil, etc, all require ABS on new motorcyles.

Would you prefer to read a full list of EU member countries instead? As well as Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain and Sweden, ABS is also required in the UK.

...but it has mostly harmonized road rules, eg in relation to the ABS on the bigger bikes.

I'm in South Africa, and most of the popular brands have ABS by default, including top sellers like BMW R1300GS, Honda Africa Twin, KTM 890. This is big adventure country, like Australia. I think the superbikes also have ABS now since about 10 years ago.