[nabla9]

Lack of ambient light and atmospheric attenuation. Significantly more direct light vs indirect light.

If you fly at 35,000 ft the horizon is at 221.3 miles and most of it is dense air. If you look directly downwards from ISS there is less than ten miles of thick atmosphere between the camera and the target.

If you do ray tracing from single light source with few objects and without effects that simulate atmosphere you simulate how the scene looks in vacuum.