Frustration mounts

I've noticed a couple of these this year: Return to Sender labels attached to letters that have been correctly addressed and sent to people still living at the said address. Incredibly frustrating. And, as you might expect, I have theories.

1) My writing is appalling.
2) The people employed to deliver these letters cannot read.
3) The people employed to deliver these letters cannot be arsed delivering them and so stick a RTS sticker on the envelope just for the hell of it.
4) The people employed to deliver these letters are overworked and stressed and so stick a RTS sticker on the envelope to save time.
5) The people employed to deliver these letters are complete bastards and think the idea of someone writing to someone else is anathema to civilized lifestyles.

Probably just my handwriting though.