why track or motorbus has much wider tyres?

Question

thrust and pressure.

Answer 1

Mike covered it all except the wider the tire the harder it is to tip over at a reasonable speed. The wide footprint with a vehicle with a higher payload balance keeps the truck stable on a turn.

Answer 2

Lets assume you mean truck or motorbus.
These vehicles are heavier and have higher torque engines.
A wider tire allows more weight to be carried within the limits of the strength of the tire rubber and cord - the tire can not be made extremely thick because of heat build up on the road.
Having a bigger footprint also increases friction so that the torque of the engine and forces of braking can be applied to the road without spinning the wheels.

Answer 3

yep