People are taught to do that so, in the event they get rear ended, they don't get pushed out into traffic. You might just be retarded.
Is it a big danger? Not at all. But it also costs people nothing to give a bit of extra space. Nobody is handing out prizes for being the closest one to the line. What a stupid metric to judge people on.
If nothing else it is a representation of the author's perspective on the world in which we live, and with that insight there are many interesting things we can learn about our world when compared and contrasted with our own perspective.