One possible problem is that many of the new laptops, all-in-ones and desktop components have pretty high prices in the US. Prices that are already pushing what many people are willing to pay. Then you factor in our crappy local prices for that same stuff and it's just too expensive.
A basic 15" MacBook Pro with TouchBar and 256GB SSD is R39899. That's $3366. The already eye-watering price in the US is $2399. A 40% premium on that figure ruins the value proposition, and that's not even accounting for purchasing power parity. Using the Big Mac Index converter, $3366 in SA is the equivalent of around $7000 in the US. I don't think Apple would sell too many there at that price.