In any vehicle
The «sprung» weight is the weight of the part of the vehicle and its payload which is held up by the springs.
When a bump lifts a wheel up, the spring compresses. After the wheel passes over the bump, the spring pushes the wheel back down into contact with the ground. In the case of a vehicle
If the wheel is heavy, the spring will not be able to push it back into contact with the ground as fast as the same spring could push a lighter wheel.
If the rider is light, the spring force will also be light, so it will not be able to push the wheel back down as fast as the stronger spring that would be used with a heavier rider could push the same wheel.
If the rider is light, but the spring is strong, the rider will not get enough benefit from the suspension, and the strong spring will lift the rider as well as the wheel.