Audiobook Tab Missing From iPhone Sync

I ran into a problem where the Audiobooks tab was missing from the iPhone sync page in Finder. No matter what I did I could not get it to show up.

As it turns out, the solution was more simple than it seemed. Basically, I did not actually have any audiobooks available in the Books app to sync. Once I downloaded a few from Audible and added them to the Books app, the tab appeared as expected.

It was annoyingly simple, but it stumped me for a long time and even Apple Support didn't have an answer for me.