Pietersburg was located in the Northern Transvaal, a sparsely populated rural area of farms and game reserves. Agriculture was the primary industry. Likewise, it was a stronghold for the Conservative Party, who were further to the right than the ruling National Party. There really is not much more to it, rural farmers typically held more entrenched views about racial segregation. Afrikaner nationalism placed on a pedestal the idealised version of the "volk", with self-sufficient farmers being part of that. Couple this with a strong "Boer" identity stemming from when Transvaal was an independent state, and you had an intensely traditional and conservative population in both rural areas of the Transvaal and Orange Free State. Rural communities tended to be less conservative in Natal and Cape Province due to a somewhat seperate identity stemming from British colonisation, for example many farmers in Natal were from Scottish descent, and in Cape Province Afrikaner farmers were almost aristocratic in a sense.

White farmers in Pietersberg potentially had more to lose, i.e. their property and cheap labour, than a professional in Johannesburg had to lose by the end of Apartheid. Coupled with their identity and political beliefs, they voted no. If you look across South Africa you can see similar patterns, i.e. in the Orange Free State, with Kroonstad also being close.