Because most of the times driver who delivers the parcels just puts a letter in the mailbox saying pls ch ollect from the office branch. I am a disabled pensioner I am in bed alot and Mt bedroom wi n dowsing I can see them. They never knocked. Same for the daily mail man I have chased him in my nightie till I catch up a few houses down to get my parcel and sign for my parcel. Even the drivers who drop off mail first I hear mail man then by the time I have gotten straight up got to the door to see her little red car already reversed and just taking off.