I think a large part of it comes down to laziness, really. How hard is it to get out of the van and at least try and knock on the door?
BTW, the only courier company (as far as I know) that delivers to the Post Office is Courier Post. They also allow deliveries to PO Boxes.
I feel they are under pressure timewise, so a few 'auto" cards are a time saving. I understand that, but ITS NOT MY PROBLEM