The answer, of course, is organizations usually are not designed from the ground up in such a manner. They evolve over time, focusing on immediate business needs and addressing specific, narrowly scoped problems. The goal may be business modularity, but all too often the actual actions continue to support fragmented architecture.
I once worked for an organization that had twenty four ERP systems. Twenty four. Nobody designed that, nobody wanted that, but there we were. They all came by mergers and acquisitions of companies that themselves recently merged with or acquired other companies. The technologies involved ranged from VMS systems running on (proprietary, or course!) DEC hardware to a version of Apple's FileMaker that was released in 1994 and everything in between.
"In most cases, systems built to achieve immediate business needs have become expensive, redundant, and difficult to maintain." (Ross 93)
Needless to say, it was a challenging environment to support. And great progress made to achieve the lofty goal of "One ERP." One by one, these older systems were sunset, their data migrated over to the organization's architecture ERP solution, but the biggest error was that many of the older systems were allowed to linger, in read only mode.. They were all running on horribly out of lease/owned hardware and nothing had official support, so there was no cost. What wast the harm, right?
The trouble was, the user base didn't stop using them. Any sort of change is difficult and many many users simply refused to use the designated tool and continued to leverage the legacy systems. And man, were these folks dedicated. Unofficial 3rd party applications were brought in to support the older environments. There were a few cases were some code was hacked together. And when this illicit tech stack would break, the losses in revenue could be measured in the millions. This was allowed to continue by executive leadership for far too long, squeaky wheels get the grease I guess. It was only Windows XP going EOL and the mass exodus to Windows 7 that came after which finally toppled the house of cards, since the clients for many of these systems would no longer function.
I think the lesson here, is that EA needs to not just be about the management of technology...it must also be about managing people. "If you build it, they will come" is only is guaranteed to work for Kevin Costner.

