This flows naturally from US copyright: all creative works are copyrighted. If the documentation is not explicitly licensed, then there is a risk that your dis

This flows naturally from US copyright: all creative works are copyrighted. If the documentation is not explicitly licensed, then there is a risk that your distribution of the documentation is a violation. This solves the problem of unknown documentation licensing, and makes the documentation a copyleft work product of its authors, which guarantees that any future derivative work that is released is also under a liberal license.