By the way, why does the old passport you submitted get sent so separately and delayed? And why are there so many passport processing locations?
Is it that certain offices only intake the information (and later return the submitted materials to you), while a few others actually put the books together? Does this produce more efficient handling?
Yes, it is mostly for efficiency that different offices handle different parts of the process (receiving the old pp, sending out the new pp, etc). Why so many offices? Well, they process on the order of 22,000,000 applications per year. Almost 2,000,000 per month. That would be one huge center if all were done at one place. So they have many regional centers to smooth out the load and reduce postal delivery times. Also for security - if something happens at one location (fire, tornado, physical plant / maintenance issues, etc) processing can continue - dont put all your eggs in one basket, yes?
The expired passport gets scanned into electronic storage - so it needs separate processing/handling completely different from that needed to produce a new book.