What is the primary reason the faint, scattered starlight reaching Earth at night often fails to register as distinct illumination?
Answer
The faint, scattered light is often just below the perception threshold of human vision.
The human eye has an absolute threshold below which it perceives nothing; the faint, scattered light from billions of distant stars that crosses space often falls below this level when the bright light of the Sun is absent.

#Videos
Why Does The Sky Change From Blue To Black? | Earth Science
Related Questions
Why does the daytime sky appear blue?Which property of light is scattered most efficiently by tiny atmospheric particles?Why does the sky not appear purple, even though violet light scatters more than blue light?What causes the sky to appear perfectly black when viewed from a location lacking a substantial atmosphere, like the Moon?What observation regarding the night sky serves as visual evidence that the universe may not be infinitely old?How does the blackness seen at night on Earth differ fundamentally from the blackness encountered in space?What is the effect observed when viewing the sky from a very high altitude, such as a mountain summit?What determines the perception of brightness in the sky when an observer is within Earth’s atmosphere?What causes the human eye to temporarily perceive the night sky as profoundly dark immediately after stepping out of a brightly lit room?What is the primary reason the faint, scattered starlight reaching Earth at night often fails to register as distinct illumination?What is the fundamental conceptual distinction between the daytime blue sky and the nighttime black sky?