Yes, exactly. Does the average EV driver really want to make sure their car sits outside all day, with no shade, every day, in order to take advantage of solar cells on the roof? Well, no doubt there are people who would do exactly that. But likely most people wouldn't, and it's certainly not an optimal way to treat your car.
As Elon Musk says: The best place for solar panels is on the roof of your house, not the roof of your car. (Altho solar panels mounted on a stand-alone frame in your back yard is even better for most installations, but that's quibbling.)