1. Australia has pretty limited data pipes to the outside, so the more traffic is kept in-country the cheaper it is and the less likely there will be issues with world-traveling traffic
2. Aus ISPs have pretty low quotas for international traffic (40-200GB range I believe) but none for national traffic[0], which also lead those same ISPs to build or help building massive national caches of international resources (I believe Steam download traffic, for instance, is kept mostly or solely national)
[0] I may be wrong, and please correct me if I am. That's what I recall from past conversations on the subject