This article gives a deep dive. Honestly, the production change was so unnecessary because all it did was change the order in which they did things. I don’t know how this will have sped up the process of building the plane
The article doesn't give a deep enough dive on its own to understand really what and why.
I've got some exposure to manufacturing planning, and when I read the description it immediately jumped out at me that whatever the exact part in question was, it most likely was being fabricated to overall shape, coated, and then holes drilled.
Perhaps this is the sort of part that previously did not have the holes drilled until installation, which due to the size of many of the parts and how tight the tolerances often are, is common in aerostructures. Or possibly drilling post-coating was specifically for the grounding path, and there simply was not clear enough documentation kept or a thorough enough documentation review done (assuming the current rack design was implemented in the NG, we're talking about records going back 20 years) to catch that when the fabrication change was decided on. What we do know is that the change was made early in the grounding, before Boeing seemed to have taken the message to heart that they need a renewed emphasis on thoroughness.
Regardless, machining a part, coating it, and then sending it back for more machining is extra work. Drilling upon installation, if that was the original method, is even more work, slows down final assembly line flow, and creates extra FOD control requirements. I know not just Boeing, but also Airbus, Embraer, and all the structures suppliers are regularly looking for opportunities to reduce the complexity of fabrication and assembly plans for cost and time savings, and opportunities to reduce FOD in the first place.
The Gates article quoted a FAA source as saying that this was "a minor design change that did not require regulatory approval" and now FAA would conduct an audit of Boeing's process for making such design changes across its product line.
Seems they have conducted a successful CYA maneuver.
The CYA maneuver would be "The FAA verified Boeing has a process in place for making design changes and wrote a sternly worded letter that the process should be followed." Auditing the processes means reviewing how they are intended to work and whether that is sufficient, and verifying they actually do follow the processes. It should also include for this instance, determining how the escape happened.