I suppose it is all last minute mail posted too late to arrive before Christmas and probably the mountain of insufficiently addressed mail that either has to be returned or try to deliver.
I always marvel at how well the post office does in delivering badly addressed mail.
I have received goods at work before with just my name on them no company name and only part of the industrial estate address. I think it helps that the postman sort at the local office their own particular deliveries so they get to recognise names etc.
I don't know about your country...but in this country postal workers are considered only a slight bit higher on the food chain than migrant workers...LOL
But, I dare say that before my Mom died, I could put a card in my mailbox for 39 cents on a Monday, and it would get to her mailbox in another city in Texas the next day, and THAT is a pretty good service to people.