The perception that faraway objects appear to move slowly even when they are actually moving quickly is a result of the way our brain interprets visual information and depth perception.
When we observe objects in the world, our brain relies on various visual cues to understand their position and movement. One of these cues is called motion parallax, which is based on the apparent motion of objects as we move relative to them. When we are stationary and observing objects that are far away, we experience very little motion parallax because the objects are so distant that the change in their position relative to us is minimal. As a result, our brain perceives their movement as slower.
On the other hand, when objects are closer to us, they appear to move faster because the change in their position relative to us becomes more pronounced. This is why objects passing by when we are walking or driving seem to move quickly.
Another factor that contributes to this perception is the relative size of the objects. When an object is far away, it appears smaller than when it is close. Our brain uses this size difference as a depth cue, and since we know that larger objects tend to be closer to us, we interpret the smaller size of a distant object as an indication of its distance. This further reinforces the perception that the faraway object is moving slowly.
In summary, the apparent slow movement of faraway objects is a result of motion parallax, the relative lack of visual motion cues, and the perceived smaller size of distant objects. These factors combine to create the illusion that distant objects are moving slowly even when they may be moving quite fast.