Large consulting companies like Accenture have entire divisions of their business devoted to "government". These divisions make money by developing software for governments. It is very much against their interest for this software to be open source because 1) there is visibility into their performance and 2) they can't sell very similar software to the same government if everyone knows what software they've already built.
These are the real vested interests preventing this code becoming open source and why lots of government agencies who do their own development are perfectly happy to release the code or access to their APIs.