The caps are one of the many stringent border controls the country has adopted in its battle against COVID-19. The government has banned foreign travelers from entering the country and barred its own citizens from leaving since March, meaning those looking to return under the cap scheme are Australian citizens and permanent residents.
Many have no jobs, no visa, no healthcare, no access to welfare, and in some cases, no permanent roof over their head.

https://edition.cnn.com/travel/article/australians-stranded-abroad-christmas/index.html