Comment by sam1714

In the 50s, when they started to use machines to sort mail, there were keyers at every facility that sorted mail. I believe there are still are still some local keyers on parcel sorters, where it's harder to "lift" the image of the address on a large box.

For letter encoding, they used to have 55 centers, in 2014 it became one, in Utah. A large part of it is OCR getting better and deciphering most handwritten addresses.

Another part of it is simple consolidation: it's trivial to send images over networks, and due to how mail has to be sorted together for dispatch, the demand tended to be peaky. Consolidation lets you exploit different timezones. (Slowing down the mail also gives a big benefit because you can spread the load over the whole day)