Why is space black?
During the day light travels from the sun towards us and is deflected and scattered by all the molecules in our atmosphere, so the whole sky lights up. At night, we are facing away from the sun so can't see its light. We can see its light reflecting off the moon though.
We do see the light that has reached us from stars, but only from the stars close enough for their light to have reached us yet (given the age of the universe, the rate of its expansion, the speed of light and the fact that light becomes dimmer the further it tavels.) When no light reaches our eyes, they see black.