I used to work for the USPS many years ago - I know that sometimes, they have a process which makes no damned sense - and you find your letter first going to a large processing center far away, just so it can be sent back to another place, close by. I recall in some regions, large parcels ALL went to the big facilities in that region - even if it was just going across town.
I know I've seen this with Amazon packages - watched my package go from town to town, when if my package took the most sensible direct route, it would be faster.