Why does binocular disparity become less useful for judging very distant objects?

Binocular disparity, also known as binocular parallax, is a primary cue for depth perception that relies on the slightly different images each eye receives due to their separation in the skull.12

This mechanism becomes less useful for judging very distant objects because the angular difference between the two retinal images diminishes as the distance to the object increases. Essentially, as an object moves further away, the lines of sight from the two eyes become increasingly parallel, reducing the disparity that the brain uses to calculate depth. While this cue is highly effective in near space, it loses its sensitivity at greater distances. To overcome this limitation, optical instruments such as range-finding devices and stereoscopes can be used to artificially magnify the parallax distance between the two eyes.21