Moon and another attributes of the real Earth. Why?

[Kitfox]

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

There's plenty of imagination used in Eorzea to make it different from Earth, the elements just don't break basic life support. You're in the wrong game and genre buddy.