The light makes it harder for the driver to see at night.

Light inside the car reflects off of everything in the car, sometimes including the window. If it's dark outside, this might mean the driver cannot see anything outside of the car. Also, the sudden change in brightness might cause the driver's eyes to adjust, trmporarily blinding them.

Generally, it is best if the driver can see through the windows and outside of the car.

Biochemically adjusting to a brighter environment takes the eyes a fraction of a second, but adapting to a darker environment takes them 20-30 minutes. This is the reason pirates wore eyepatches despite both eyes being intact, you can enter the belly of a ship and have at least one eye already adapted to darkness.