The pressure that's seen on the sidewall of a tire is the MAX pressure that the tire manufacturer recommends for that tire. That's because that tire can be used on many different kinds of vehicles. So while one vehicle may have a tire pressure recommendation from the vehicle manufacturer, when applied to another vehicle, the tire pressure recommendation from that manufacturer might be different. So the tire manufacturer designs that tire to be applied to many different kinds of vehicles.
Vehicle manufacturers run extensive tests to determine what tire pressures should be used to provide the best ride, handling, safety, and tire life when those tires are used on that vehicle. And this is why you always follow the recommended tire pressures that the vehicle manufacturer recommends.