I always assumed it was to cut down on the amount of work for the level designers, particularly with interiors. The two walls closest to the player (bottom of the screen) are usually lacking the detail compared to the top two (which will usually be riddled with things to interact with).
When screenshots of their game pop up, I'm sure they want people to see this:
img1
instead of what's on the opposite side of that room:
img2
..as the latter has the potential to hurt sales.
I see you point. But my argument was actually purly my own opinion. I don't mind the "not so perfectness" of image 2. But again, I see your (and therefore Larian's) point.
