Because the Afrikaners are principally Dutch Reformed Church. There is also a good sprinkling of Huguenots [French] among them which explains the French names among the Afrikaners. One of the reasons for great wines coming from South Africa is that the Huguenots took French wine-making techniques with them to the Cape.
Re French last names...yes indeed;however, when they fist fled to The Netherlands, the Dutch influenced them to change the spelling to the Dutch way. LOL
But yes, you CAN pretty much still tell WHO, by their last names, were the Huguenots who were living in The Netherlands and went to what is RSA on the very first voyages.