Question

Give reason: the vehicles are fitted with shockers

Answer 1

For your comfort and safety. If you go over a bump without dampers in place the springs will simply oscillate. You will get an uncomfortable bouncy ride and the car will have less available mechanical grip for turning and stopping.

A damper (what you call a "shocker") resists the bounce by forcing oil through narrow openings. The energy of the spring heats the oil inside the damper instead of bouncing the car up and down.

Answer 2

Vehicle receives the sudden sharp movement when it moves on the uneven surfaces. 
So, the vehicle receives the impulsive force .
To minimize this impact , shock absorbers are used.

Impulse=F(Δt)
Fα 1/Δt

The shock absorbers increases the time of sudden sharp movement  thereby reducing impulsive force.
This minimizes the  damage. to the vehicle .