Because the Volt and Leaf are
Because the Volt and Leaf are not electric cars. At the end of the day, they are still gas-powered cars that do not have the level of self-monitoring that the Model S has. A check engine light is not a fire alarm that shuts down the car. Their construction is not far removed from the rest of the Chevy and Nissan lineup, and the passenger cabin is not as well protected against catastrophic fire as the more expensive Tesla.