Standard map projection strikes again. Starting from the tip of South Africa, it’s 4300 miles to Uruguay (where you’d land straight east) and 5300 to Perth, Australia. New York City is 3300 miles to Portugal and obviously the smoothest route to Australia is hopping through southeast Asia. Coincidentally, the northern hemisphere has way more population.
Cape Town is only 34° south. Going to 34°N, you’re lined up with Los Angeles, Dallas, and Atlanta USA, then Morocco, Algeria, and Tunisia, then the middle of the Mediterranean Sea, Lebanon, Syria, Iraq, Iran, Afghanistan, middle of China, southern tip of South Korea, and grazing below Tokyo. It’s still 4100 miles between Georgia (USA) and Morocco.
There are no southern polar flights and no southern undersea cables because the southern continental points aren’t as far south as the northern points are north. Population volume doesn’t create the demand for more direct service.