why do heavy vehicles have broad tyres?

Wide tyres are used in heavy vehicles like truck to spread the force over the large area of contact and pressure at a point becomes low since
pressure= force/area
So, larger the area in contact lesser the pressure in tyre and more is grip on road because the weight of truck is spread over the area
One more example is the tracks of trains in between two rail lines, there are lots of horizontal wooden timbers or tracks for the same reason.