Because it requires low power, and the belt  has a longer life.
Slider bed is used for loads with small, irregular bases, conveyor loading areas, and  next to operators such as assembly stations, because it  does not have high speed traveling and heavy load capacity.

Digidale Belt conveyors are most economical solution of transporting bulk materials at high rates over great distances.

Belt conveyors are used for horizontal, inclined and declined movement of loads.

The belt is supported on rollers or on slider bed plate.

Roller bed is usually preferred.

In the modern material handling systems the most popular belt conveyor systems are

*   Flat Belt Conveyors
*   Throughed Belt Conveyors
*   Cleated Belt  Conveyors 
*   Side Walled Belt Conveyor