PERGO flooring for public spaces

This flooring has fire safety signage imbedded in its pattern. Selected white lines are printed with 'glow in the dark' ink, which is charged by ambient lighting.

In lit rooms, the appearance is of white on grey, but when dark, glowing arrows appear, pointing to the nearest fire exit.

Why is standard fire signage placed on walls and above doors, when in a room filled with smoke, the most visible surface would be the floor?