I think the main counter-argument is that people like to organize in static systems? Even if you use tags, you almost certainly want to restrict the specific tags that you allow so that you don't have a data science/cleanup task of normalizing things later.

Tags also fail because people then want to categorize their tags. Which tag is the author's name, versus the editor's? Publish year, versus year I read it? I suppose we could say that people want "slots" not "tags"?