Simply, there is no 'void' in the chest of a deer.There is a pleural 'cavity' but it's notbig enough on a healthy deer to squeeze a broadhead through.

On the other hand there are all sorts of places you can put an arrow into a deer and not kill it.

The spine lies much farther down that most people realize. Most so called void/no man's land hits are above the spine. The arrow hits the bony spinous processes and transverse processes of the vertebrae and that's why the arrow fails to completely pass through the deer.

The shape of a deer's chest cavity means that an arrow that manages to slide in right under the deer's spine will hit lung. The dorsal aorta lies under the spine too.

I think these aresome goodpictures showing just how low the spine dips.
(The farther forward, the lower the spine) The arrow is embedded in the spine.