Even though farmers almost never vote Labour, National may get sympathy votes from others if the farmers jump up and down about how family homes for most people are exempt but not for farmers since it's typically one title.

There's also the extra challenge of farmers claiming a worker's residence is not a rental, then sometimes it will be on the same title as the main house and sometimes they bought the neighbour's farm and the houses are on two different titles so might get treated differently between farms.

I can see how it's easier to exclude them and then expand later if needed.