
Maybe its not a moon... it's a space station!

That's no moon...
Moons in the MEU are almost always the wrong size. Most moons you see up in the sky of whatever planet you are on, at least in ME2, are way too big. Unless Shepard is actually on a moon and that thing up in the sky is actually the planet it is circling. As big as they appear to be they would be so massive as to quickly collide with whatever they are orbiting, the gravitational attraction would simply overwhelm whatever speed they are orbiting at, considering they are moving too slow for us to see.
Because, it was lonely?
I doubt that is even Earth to be begin with. I can't even tell what continent is facing. Not to mention that if it was earth you would have seen lights and stuff.
the planet looks like Virmire, actually.
This was discussed once (and in typical BSN fashion, blown hugely out of proportion over whether the planet was Earth or not).
To answer the question: Artistic License.
It's not realistic, but it does look cool.
Meh. I'd be more concerned if the sun was too close.