It’s random too. A site that doesn’t work for them works for me, and vice versa.
Unless you're in WA, your international traffic is almost certainly going out via Sydney.
Up until about the last 18 months, all the cable landing points bar one were in Sydney.
Since then there's been a couple of new high-capacity links landing in WA, and another in QLD.
But most traffic is still US-Bound, so Sydney makes the most sense for a location to host in as the first point.