> replacing the method of propulsion, does not fundamentally alter how you build it, or how you source the parts to build it.
There are fundamental changes in car design. No need for a huge tunnel and axle in RWD cars, and no huge, loud, hot and vibrating engine in the front. In addition the battery pack shifts down the centre of gravity (thus making the car way better in handling curves), and the now free space in the front (what Tesla calls "frunk") is a huge crumple zone.
Also, with the engine there goes a huge complex part with many different highly specialized suppliers - granted, it's replaced by another set of parts, but fundamentally it's orders of magnitude less parts, and easier to install.