It's a union thing, actualy three unions. In order to process local mail the post office would need a "postal clerk" to sort the mail, "window clerks" are not allowed to do this only handle pre-sorted mail. Likewise "letter cariers" only handle pre-sorted mail to merge with bulk advertising etc before delivery.I think one of the other change that seem non productive is the removal of a slot to drop in the Post Office mail that will be labled local mail
Everything gets dropped into out of town mail...and many slots for DVD's. But that could be a move for job security.
At least that was how it was in 1997 contracts may have changed but I doubt by much. The more USPS automates the harder the unions dig in to protect jobs by no allowing crossover work. Of course you have the "mail handlers" who move the mail from the loading dock to the clerks.
It's really quite amazing how they have each others backs. Sixhunderd page books covering every little detail from lighting to temprature to bathroom breaks. Then there are several levels of managment who are selected from the most dimwitted sheep to follow orders. Most of the managers I worked with could not even write a memo.
One of the funiest things I saw was when they assigned a deaf mute clerk to the pickup window for the postboxes, or the window clerk who only spoke chinese and nodded her head a lot. I can laugh about it now 12 years later but I could clearly see why some workers "go postal".