Why don’t they walk on the sidewalk?

After our first decent-sized snow in Lansing this weekend I broke out the snow-blower.  Yesterday afternoon I fire it up and do the driveway & sidewalks.  Then, go around and sprinkle salt to make the sidewalks as safe as possible.  I live on a corner in a busy neighborhood so there is always lots of foot traffic.  On my way to work this morning, I notice footprints all over the yard!  It seems everyone would rather walk across the yard through the snow than use the clear sidewalks!  Why do they do this?  I guess it shaves those valuable 7 seconds off the walk not going all the way to the corner and turning?