In iTunes 12.2, the latest version of the app, audiobook display by author is broken. When you select this view, and select either All Authors, or a specific author, nothing displays in the right-hand pane of the iTunes window. A few people noted this on Apple’s support forum, and I confirm that it’s happening to me as well.
Here’s a few audiobooks in my test library:
And when I choose the Authors view, here’s what I see:
This seems like a dumb bug. iTunes should be tested for the most basic interface issues. Let’s hope Apple fixes this one in the next update.