As a delivery driver, it's just force of habit. Even if you put a note on your order, we've just done the same thing 20 times before we get to your house. It's automatic. Better to put a sign on your door. Maybe say you have a sleeping baby or something and you don't want to wake them up. That way hopefully we see the note as we're about to knock.
Yeah I totally get that and I'm not actually mad at anyone who does it. It's just annoying, you know? But it's not like there are robots coming to deliver stuff to my house, it's humans. It's fine.
Completely understandable. But for those of us that would prefer to avoid interacting with people, playing into human nature can help. We'll forget the note in the package the second it's been scanned and ready to deliver. We'll usually stop and read the note on the door at eye level just before we knock. A little social engineering can go a long way.