Answer:
Light pollution
Step-by-step explanation:
Light pollution Is the artificial light from a variety of things-- commonly street lights and building lights that reflect on the sky; cities are a great example of this, and in most photos of cities barely if any stars are visible along with the sky being brighter in some places- that's actually the artificial light blocking out the stars and making the sky appear brighter. (the severity ranges from place to place)
Quote:
"What has happened to the stars?
Of course, they’re still there, but we can’t see them because of light pollution: the excessive and misdirected anthropogenic and artificial light that has invaded our night skies."
Conclusion:
The reason why the sky appears mostly black is light pollution, it not only covers the stars but sometimes makes the sky appear lighter than it should be-- on top of this light pollution has many other negative effects on the environment.