ND goes against our objectives.
Our objective is not only to redistribute works, but also to allow them to be reused (modified).
The only example of ND that I think Wikisource could accept is works which are required to be reproduced faithfully by law or similar. For example, the legal code of most Commonwealth countries is protected by law, and some of these nations have licensed the legal code under a "ND" like license.
The legal code is not created in a competitive environment. There is only one for each nation. If we dont accept their ND license, there is no chance that an alternative could be written.