Because the gameplay in NnT is so heavily dependent on what you can and can't see. Chant suppressor and possession radii are determined by what you can see. "A little bit" might be counter-intuitive in places.
Also judging from how some of the backgrounds look, they're based around very specific cameras and viewports. It may seems silly, but adding height might actually be significant with how the scenes are layed out. Some of the camera paths would probably need to be rejigged slightly to keep the same look and feel.
|