Why do they ride on the gas tank?

 I've noticed that delivery men ride on the gas tank of their scooters and sometimes they sit on a pillow. Does anyone know why? 

They believe that their

They believe that their scooter will have more torque and go faster is they shift their weight forward and away from the rear wheel because motorbikes have rear wheel drive. 

Torque

 Thanks. This makes sense. The amount of available torque is determined by traction.  During heavy acceleration the weight is shifted from the gas tank to the rear wheel giving greater grip on the road.