Question

There are so many stars in space but still why is it dark in there, evethough light can travel in vacuum?

Answer 1

Most of the objects in space don't emit in the visible spectrum and even when they do, there's a lot of dust and gas in space that will absorb such radiation and re-emit it at other wavelengths.

You also have to deal with the fact that the atmosphere scatters certain frequencies and absorbs others. What you see in space is not what you see on the ground. This is just a variant of the gas cloud problem (aka black body radiation).