My Argentinean Malbec kit also came with sorbate and no f-pack. I think it is just kit makers insurance. They are targeting a wide audience with varying experience and not everyone follows the instructions all the time. The use of sorbate, imo, is to protect that small population that does not wait for fermentation to complete fully. Kit makers are incented on getting you into bottles so you will have empty carboys to fill with more kit sales. That is just my theory, but I can't think of another plausible reason for sorbate in a dry kit.
My Malbec is bulk aging on the Hungarian cubes and I did not add the sorbate, and don't intend to. I did add the K meta though as that protects the wine whether sweet or dry.