I was reading the Harvard Design Mag and this explanation sparked my interest.
"Why is architecture so often represented only from the outside? Do architects just pay more attention to the outside? Or is it perhaps because the external view of a building provides the images of totality, an image that in it's flatness is easier to comprehend than one of the interior? Photographs of the interior can require more attention. They are frequently fragments of a larger entity, like a room, with the added complexities of spatial depth and variations of light and color, materials and surfaces. Along with the particularities of the occupation of space, they often record the ordinariness of the everyday. To see the interior through the camera is to see it once removed- an artifice that says as much about our attitude towards the conditions surrounding the subject as it does about the subject being depicted."
It's a metaphor, really.