Why is the door to the public toilet empty from below? Learn the amazing reason

You have often seen in movies or dramas that any public toilet, The space under the doors is empty, ie the doors are not fully installed, but half the doors are installed in Indian films and abroad. What is the reason for leaving this empty space? Reason: This space is left empty so that if the person inside the bathroom sees someone passing by, he will realize that the person outside also has to go to the bathroom. And that's why he should get out of the bathroom as soon as possible and use the public toilet as much as possible for the public.