I would speculate that, since CC buy a reasonable quantity of oils for new kits, factory build, as well as their own workshop which services a wide age range of cars, the decision is most likely commercial. However, any supplier change will be backed up with appropriate due diligence on performance. If the selection was purely lubricant performance based, it would be unlikely that one supplier would always have the best oils for the Ford engine, Mazda box, and BMW diff.