I guess the question becomes why did Tesla have so many one-off parts? Is it all attributable to being electric rather than gas?
Partly yes, but Tesla didn't have a shelf to go grab parts from in the first place, either. They didn't come out of an existing auto company with an existing parts inventory after all. And for the body & frame they also started with a Lotus which is itself not a mass-market car.
You'll probably find _some_ non-custom common parts in a Roadster, like maybe the A/C system. But the drive train makes up a pretty big chunk of the parts in a car.