Okay, the reason is a guess, but it's proven that people aren't plugging in: see, e.g., https://cars.usnews.com/cars-trucks/features/phev-owners-not-plugging-in

Okay, the reason is a guess, but it's proven that people aren't plugging in: see, e.g., https://cars.usnews.com/cars-trucks/features/phev-owners-not-plugging-in https://cars.usnews.com/cars-trucks/features/phev-owners-not... and https://www.autoweek.com/news/a60383277/wltp-phev-data-gap-report/ https://www.autoweek.com/news/a60383277/wltp-phev-data-gap-r...