They're part of the same ecosystem that deals with how we build and manage our societies. Legislation is the instrument used by our societies to manage themselves. Parliaments are the law-factories, if we can say so, and more specifically debates, committees hearings and reports are the assembly lines where laws are finalised. And it is the judiciary where the relevant part of laws may be applied and so the place where we can monitor the impact of laws and parliaments on society.
Having a standard that deals with the whole ecosystem of laws, from drafting in parliaments to its applications in the courts of justice just made economic sense - that is to say, considering the re-usability of documents, and it made social and political accountability sense.