Firstly, there are many international links from Australia to the rest of the world, and most ISPs do not use all of them, just a selection, which means various ISPs will have varying speed and latency depending on where the destination server is in the world. Secondly, these links are capable of huge bandwidth (eg last I checked the AJC is capable of 10000gbps), but these are huge bundles of fiber links, these individual strands may be leased out to providers, or shared among whole groups of them, with usage split by wavelength, or limited by quotas or prioritization. While only a fraction of the whole cable bundle is being used, the individual strand(s) being leased by the backhaul provider who supplies your ISP and half dozen others may only be capable of a few gbit, and your ISP may only pay for a 10% slice of this. They could pay for a bigger slice or more fibers, but often don't, because only a small selection of their customers will actually understand whats going on and that they're being ripped off. As such it's really not a question of Australia's international bandwidth - if the demand is there from providers, the bandwidth will be made available for purchase - but for providers offering 100mbit/1gbit "unlimited" connections for under $100/mo, and NBNco taking a sizable slice of this just for the end connection, the ISP may simply not be able to afford sufficient bandwidth to keep it's customers running at full speed. This will vary based on ISP, depending on their overheads, their profit margin, and the usage profiles of their userbase. Once an ISP gets a reputation as being "great for international performance", heavy users tend to flock towards it, saturating the international bandwidth the ISP pays for, and making it bad for international performance. At this point the ISP can either purchase more bandwidth, change their plans to include a data limit or shaping, or just sit on what they have and allow the contention ratio to get worse and worse, allowing their profits to increase.