Why the big tires?
Larger footprints gives lower ground pressure so you can drive on softer grounds with minimum disturbance, no matter if the ground is snow, dirt, sand or anything else.
Larger tires give higher ground clearance, making it easier to drive over rough surface, rocks and snow.
Large tires rolls easier on rough surface, with the tires eating up more of the surface irregularities. The tires give better ride and less load and forces on the suspension of the car.