The question is easy to answer; South Africa was formerly part of the British Empire, which decreed that the rule of the road was to keep left in order to avoid collision, end of story.
NO not the end of story. The real question to be asked, is why does Britain (and her former colonies) drive on the left, when 65% of the countries of the world drive on the right?
If one goes back 2000 years, it is highly probable that the Romans travelled on the left as proven by wheel ruts discovered by archaeologists at a Roman quarry near Swindon, Wiltshire, England. The ruts on the left were much deeper than those on the right, suggesting that the carts, heavily laden with rock, were leaving the quarry on the left.
Although the Western Roman Empire collapsed in the fifth century AD, the Roman Catholic Church arose to become the authority controlling Western Europe. It is highly likely that as the Romans had built the major roads of Europe (all roads lead to Rome), the status quo remained during the dark ages and when in 1300 AD, Pope Boniface VIII gave a Papal Edict telling all pilgrims travelling to Rome to keep left, he was only reinforcing the general custom.
The upheaval wrought by the French Revolution brought about, in 1794, a rule to keep right instead of the traditional left (France being a Catholic country it is reasonable to presume that prior to “Le Revolution” they abided by...