Well, from my own experience, this is the time of year when those contractors who barely did their jobs at all previously, jump off that cliff...
But no, I wouldn't imagine that even bad workers would lead to something so endemic. It could be a company wide issue, or multiple people failing to meet their end of the bargain compounding - particularly if the delivery locations are different. However on that same note; what evidence is there that the packages are even leaving your local area - and its not your depot or couriers which are the blame.
Overall though, if something like this can be put down to the incompetence of a middle man then that'd be my first assumption.