The investment in parts is already made. All they need to do is not scrap the tooling. Until the car the part went to is 15 years old that isn't worth doing as you will make more from selling parts than from the cost of storing the tooling. Common parts like filters will be around for much longer. Parts that rarely break will have the tools destroyed sooner, but with millions of ICE cars on the road there will be a lot of needs for parts even if the need is less than today.