Whilst it is annoying that this happens we are British people resident in the UK who have visas. We do not have any rights in Australia and nor will we have any until we live in Australia as residents.
Although Australian employers do offer jobs to overseas residents, and the lucky ones get help with relocation, they are not under any obligation to offer employment to overseas residents, it's their choice, even if the job is advertised overseas as well as locally.
UK law does not apply in Australia the same as Australian law does not apply in the UK.