South Africa has several reliable airlines. As others have mentioned Airlink is generally very good and very reliable. FlySafair is the largest carrier by passenger numbers and again very reliable (they offer around 20 flights a day between Johannesburg and Cape Town) - more along the South West style than a legacy carrier. Lift is also not bad (but I personally find the legroom too tight). I also enjoy CemAir because the older style leather padded seats I find give more room. I think suggesting that there is no reliable internal carrier in South Africa is a little unfair, just because there is no "main national carrier" - just like in the US there isn't a single national carrier. There are very frequent flights available on the JNB-CPT route and on the JNB-DUR route - linking Johannesburg to the country's second and third largest cities.

In your instance Hoedspruit services are limited and largely there to service the safari industry with agriculture and mining in the mix. However, it really is a rather small airport (the actual commercial airport side not the military side) with limited connections aligned to the demand.