Certainly private company secrecy and many other regulation recommendations do play a role in forbidding access to details.
However, there is an overall aspect in this that also directly links to the highest possible level in politics.
According to some people I had the occasion to meet, the space capabilities of a nation, and its associated strategic power, are judged by several levels:
1) the capability to launch a ballistic rocket correctly (which is the actual key ability to develop strategic nuclear power);
2) the ability to manage re-entry issues (which is key to man mission);
3) the ability to do a rendez-vous (and docking) with an existing object already in space (which is currently considered the final step in the ability to build a spaceship).
Whenever you address any of these steps in whatever level of detail, so many VIPs step in to remember you the importance of the issue... My biggest surprise is the fact that it has been admitted that Linux was used for all this.
In fact, that's an incredible announcement: we now have in hand something linked to strategic power capability. (I wonder who will dare to volunteer as the maintainer for the seat at the UN security council?)