Because they would lose the packages and claim we never transferred them to the PO.
I delivered a main P.O. for 16 yrs. Sure post is nothing compared to the bull
involved with delivering expedited bulk/junk mail to them. I would have to wait until they processed it all.
You just have to make friends with them or you'll be miserable. I loaded everything (my main po got everything - housekeeping, maintenance, automotive, office and administrative, flags for retirees, etc) on a gondola and pushed it to an out of the way spot and gave them the run down of what was on the cart. Those two things made all the difference and they would even come off break to sign for me.