As a book agent and head of podcasts & audio at CB, this utterly infuriates me. It is a land-grab, clean and simple. A podcast is new creative content, whether or not it utilises the same topic as the book. (thread)
https://www.thebookseller.com/news/make-podcast-rights-part-your-deals-publishers-told-1222630?utm_source=Adestra&utm_medium=email&utm_term=&utm_content=&utm_campaign=Morning%20Briefing%20-%20161020

Wrapping the rights into the book deal does several things. Robs the author of autonomy.
Robs them of separate revenue. Very few authors can survive solely on their advances as we all know. If these rights are wrapped up, chances are revenue will be

set against your advance.
It is absolutely no different from attempting to keep TV rights within the book deal! Straight audio is one thing (that I don't REALLY agree with btw) but that makes more sense as it is a direct reading of the exact same words.

A podcast / audio dramatisation / film adaptation /theatre adaptation are completely new works in themselves, utilising different skills and different creative content and attract a different audience.

Let's also not forget that the vast majority of publishers have no or little podcast experience. The article says that itself - they can work with a podcast producer. Why would they do that, when the AUTHOR can work directly with a podcast producer and

keep all (or most, depending on deal and structure) IP, and between 50% and 100% of the revenue (again depending on how deal is set up)??????
BLOODY HELL. Rant over.