Most car manufacturers are in a volume game and try to sell as many uses as possible. Tesla is supply limited right now and don't have vehicles sitting on the lot. For others, the inventory itself is the responsibility of the dealers which take on loans to hold the inventory. Therefore, 0% apr is just another tool to get the units out and a back channel incentive. If dealers didn't exist, I doubt 0% apr would be as popular since everyone would be building just enough supply to meet demand.