Well, "it was a time of miracles" and space magic and the Traveler apparently adjusted the gravity on the Moon and made Mercury a habitable garden world. Also, it's called "artistic liberty". I'm surprised you're this concerned about the appearance of Mars' moons, and not the fact that Earth looked 10 times larger in the Moon's skybox than it would if you were actually viewing it from the moon. But that's more "dramatic" and in their eyes... looks cooler. And I have to agree. I mean, have you seen the HD images from the Curiosity rover? Mars seems to be a pretty damn boring place.