We've had a couple of times when they've rung the doorbell, left the parcel on the step and buggered off. I suspect that what they're doing is then delivering the rest of the street and on the way back (since it's a cul-de-sac) if it hasn't been taken in then writing out the card and throwing it in the bin.

The odd thing is it's only deliveries from Amazon that have wound up in the bin.