Why? Probably because I view toilet tissue as the first and last bastion of civilization - meaning it's (probably) the first thing installed in a new apartment, and the last thing taken when I pack up to leave (if I even go so far as to strip a place I'm moving out of that bare). So to walk into the bathroom and see that empty space speaks to me of the barren, inhospitable, and untenanted. Lonely.
[There, when that shows up in a story some day, you can point at it and say 'aha!']