My best guess is that different modules of the system get organized along the pathways of communication, compartmentalization happens wherever there is a bottleneck, and close integration naturally appears when you have the same team working on both components at the same time.

Having the same module developed by 2 teams that are on different sides of the ocean requires much more effort. So conservation of effort drives the project towards having 2 modules with well defined interfaces and are stable enough to keep required coordination down.

Intriguing. I would expect to see the unstructured organization to have unstructured code. I would also have a compartmented organization to have compartmented software. But the manufacturing company thing blew my mind.

But I like your theory, and I think it may very well be the cause for this to happen.