The tire size and tread design that was originally equipped on your vehicle may be used on other vehicles, some of which being heavier than others, therefore requiring higher air pressure for additional load carrying capacity.
The maximum pressure on the sidewall of the tire is the maximum pressure for the tire. The manufacturer of the vehicle has determined the appropriate air pressure for the application based on vehicle weight, to provide the best ride, tread wear, performance, etc. For applications such as towing, pulling, hauling, etc., air pressure should be increased accordingly.