"Is that a fault in our interpretation, in the writing, or of human society in general?"

Yes.

It reminds me of an essay I read by Ursula Le Guin, talking about The Left Hand of Darkness. Looking back, she noted how she had undercut herself by using male pronouns as the default, and other choices in the writing.

If you check the comments at http://www.jimchines.com/2014/02/non-binary-not-represented-dambergs/ I believe there are some suggestions and links to lists of books with agender characters.