How does FlySafair charge so little and stay in business?

From the Zimbabwean context, air travel is a relatively rare form of travel. Looking at the border between Zimbabwe and South Africa, around 3 million road passengers cross the border versus just 400,000 Air Passengers. There is a 7.5X gap between the two when looking at traffic volumes. So it seems quite odd that given these pre-COVID numbers FlySafair, a relatively small airline by number of routes and number of passengers, would pick up the already airline-populated Harare Johannesburg route. Moreover, it came in with a strategy that aims to lowball every other airline servicing the route.