Does anyone know why it was called the "Sugar" circuit?
My guess is the big events were always held prior to the 1950s. Before the 1950s however travel to South Africa was just too time consuming [a slow boat] to make it worthwhile.
With air travel it became a viable circuit for international stars to play. The surface wouldn't hurt, as hard courts were fair to all. Throw in the exotic appeal of Africa and audiences eager for first class tennis and I bet it was smashing fun.