I've never understood why that works. They clearly aren't slippers. They aren't sold as slippers. Nobody looks at them and says "nice slippers". Chuck Taylor importing their shoes as slippers feels fraudulent.
We had a scam in Poland decades ago, where companies could buy a station wagon with this metal grating between rear seats and the trunk [0], which was enough to classify the whole vehicle as a truck, which gave you tax breaks not available for passenger vehicles.