Because you're anally retentive, silly person!
BTW: Milk of Magnesia or Dulcolax might help.
OK, so I don't get in trouble for being a wise ass, and in the name of being a good neighbor...your name is Legion when it come to concerns about the appearance of you devices. I would suggest that you not worry about it so much...but I know that won't help much. Write it off to enjoying seeing your devices in pristine condition...and don't pathologize it...unless seeing a little scuff causes you to scream, pull your hair out, and weep uncontrollably. Should that occur...seek help!

.