Essentially Telstra (the biggest ISP in Australia) charges a fortune for transit. Cloudflare provide some detail about the relatively high cost here: https://blog.cloudflare.com/the-relative-cost-of-bandwidth-a...
Given the low total population and very low population density it's probably not really worth it though.
Contrary to the Crocodile Dundee image, Australia is one of the most urbanised nations in the world. We have almost 50% of the population in Sydney & Melbourne alone, and our top 10 cities takes this to almost 90%. While a big landmass you can reach a high proportion in relatively few spots. Assuming a business doesn't expect infrastructure/coverage for the entire population Australia not to bad density.
Obviously the general remoteness of Australia and 25m population remain big factors, and I suspect this is more relevant than the often cited density issue.