Question

why does the driver of a vehicle wipe the glass inside, even if the wiper is working on the outer surface of the glass when he drives in rain ?

Answer 1

because due to cool rain effect on the glass and a mist layer is formed

Answer 2

Typically, when it is rainy, relative humidity is very high. Your own respiration produces water and increases the level of humidity in the air inside the vehicle cabin.
The glass is exposed to water. As the car moves, air flows over the water on the outside surface of the car causing some of this water to draw heat from the glass and evaporate, lowering the temperature of the glass.
Being cooler than the interior air, the glass absorbs some heat from the interior air cooling it slightly near the interior surface of the glass. The high humidity and lowered temperature of the interior air adjacent to the glass causes water to come out of solution and deposit on the interior surface of the glass.