You're quite right that there's a decent amount of air freight between Australia and Japan. However, one thing you need to take into account is most of the air freight operations done these days aren't on passenger aircraft. Indeed, Air Canada was operating throughout the pandemic between Sydney, Auckland and Vancouver/Toronto as purely freight flights. Similarly, I reckon DHL, UPS and other logistics companies likely have dedicated flights to Japan from Australia to deal with such demand. If we agree that cargo operations remain a lucrative source of revenue for airlines due to the pandemic, why on earth would they want to haul expensive needy passengers, when they can fill the whole plane up parcels that don't complain that there's no meal service and don't post an effigy of Uncle Alan on Twitter (or this forum) when their flight gets delayed?