You've yet to address any of my responses, by the way- especially the route that I planned that, I don't know, does actually take you much more directly. Airplanes aren't like cars- a flight will only be scheduled where it makes sense. An airline will always plan the routes which make it the most money, and that doesn't include a direct long-haul flight between two non-hub airports. I understand that these routes look a bit wacky, but that makes sense when you take into account the actual logistics of airline operation.
But there are plenty of other direct routes in the southern hemisphere. Here are the largest ones I found, using
https://www.flightconnections.com/airlines.
Sydney to Johannesberg- currently in operation
Sydney to Santiago- last flown in 2020
Auckland to Santiago- currently in operation
Perth to Mauritius- last flown in 2020
Notice anything? Half of these flights stopped due to Covid. The entire airline industry, in fact, has been shifting, because airlines figured out that operating super long flights that weren't between hubs made no since. Like AATW said, 90% of people live in the northern hemisphere. Additionally, only 33% of the world's land is in the southern hemisphere, and a third of that is Antarctica. It makes more sense to route people through routes that are traveled more often, barring a few cases.
Even shorter flights are still wildly different.
Melbourne to Perth is a 4 hour flight, and on a globe Earth model it's a 1,677 mile flight. Including a half hour of taxi and hold time, and you get 1,677 miles in 3 hours and 30 minutes, which works out to about 480 mph, or a perfectly reasonable airline cruising speed.
On a flat earth it's 4,300 miles. 4,300 miles in 3 hours and 30 minutes works out to 1,228 mph, or mach 1.6.
Now if you'll excuse me, I'm off to Melbourne. I've always wanted to fly on a Concorde.
(Addition- new replies came while I was typing- the two direct flights that I mentioned which are still running operate one a day or less, so it's relatively rare to have a plane in that section of the Pacific)