Well on average, people are dumb, and the average goober probably doesn't know how to properly manage the use of a PHEV to get good mileage. It's a learning process, and the cars should come with instructions about it taped to the dashboard so that goobers will notice.

Basically you need a charger at home, and you use the EV mode for city driving, and the gas engine for highway trips. You can get more complicated to max your efficiency but the basics are simple enough for the average goober to learn. When I got one, the dealer knew a lot less about the vehicle than I did. They didn't tell me how to do anything.