And since EPUB3 metadata allows multiple authors, multiple titles, and refines on refines, what would you put there? No epub3 reader is even going to parse the ncx, and no epub2 reader takes author information from anyplace other than the opf metadata as far as I can tell.
See this older thread (from 11 years ago) for a similar discussion and explanation that epub only supports a required subset of the older DTBook ncx spec.
https://www.mobileread.com/forums/sh...d.php?t=143231