Why do the footprints on the Anjan, Rogen, and Niak tents not cover the vestibule?

On the Anjan, Rogen, and Niak tents, the optional Footprints do not cover the vestibules since the outer tents do not reach all the way to the ground. Because of the gap between the outer tent wall and the ground in the vestibule, water can get into that area during heavy rain. If the Footprint covered the vestibule area, that water could run underneath the tent.