International student intake as a ratio of housing supply is the main issue. If dwellings were being built at the same rate of international student intake, then affordability or vacancy would not be a problem.

Look up your local universities (they're all non-profit organisations with financials reported in the ACNC) and realise just how much their business model has become funded by international students. Here's a few examples:
University of Melbourne: 69% of tuition fee revenues comes from intl students
University of Queensland: 70% of tuition fee revenues comes from intl students

The universities also receive government funding, pay no income tax (because they are "nonprofit"), and don't need to contribute anything to the housing problem that they are feeding. It's time for them to help carry the burden - they should either provide housing or help pay for it.