I’d say one of the major reasons is the availability of quality grounds over the period that the cup is scheduled to run.
Rectangular stadiums around the country are pretty busy with NRL/Super Rugby, Australia doesn’t have as many ‘boutique’ stadiums as other countries do, there’s a handful in Sydney but other then that it’s down to club grounds. Some club grounds might be suitable, but in many cases the grounds are in poor shape that it’s not really worth it.
I also suspect the logistical cost of hosting it in Australia would be greater then other countries, teams would need to be spread between Brisbane and Melbourne, I’d imagine the transport costs are more prohibitive then France/Japan/Italy in that regard., notably the countries who have hosted more then once are also big football countries, I wonder if there is a correlation there because of having more boutique stadiums available through football association and the number of time hosted.