Moon and another attributes of the real Earth. Why?

[Xyno]

Realism and relatability are what make worlds believable.

World building is also not always that easy as popping another moon or sun on the sky. You'd want to know what kind of effects it would have on the environment for example. Did it ever cross your mind that maybe the human life we understand is only possible in the conditions we have on Earth? That's why most "fantasy" is still very Earth-like.

Play No Man's Sky or something if you want space exploration.

Physic- is only the conception of the laws of nature in the current world. We have our physic, but the world of the game can has different physics laws. Of course it is wise to save the main laws like gravitation and others, but why not to imagine of something new? But it is not necessary to CLONE the Earth. USE the IMAGINATION