The issue with sales has nothing to do with the appeal of the tournament (it’s still a test match against England, that has draw appeal). The issue is that SARU has significantly hiked up the ticket prices of SA games over the last two years which has made it unaffordable for the majority of South Africans.
Historically the cheapest tickets for this kind of game would probably have been around R250 or £13ish, with the majority of tickets being around R500-R1,000 (£25-45ish). Now the cheapest are R950 (£43) with a high proportion at R2,350-3,000 (£106-136ish).
That might not too high from a European perspective, but keep in mind that the SA median monthly income is R5.5k-ish (£250ish) and an unemployment rate of 33% (43% when you include those that have given up looking for work) and you can see how that amount just isn’t going to work out in the market. (Mean average income is R30k or £1.3k, but SA has significant inequality, so it isn’t a far reflection of the reality of the broader economy).
Add to that SARU have openly commented that they were targeting lower capacity (think it was like 70%) last year when they first did this, because they knew the higher ticket prices and lower capacity meant more profit than lower prices and full capacity. It’s a bit sad really.