I don't know whether it's the reason, but a super obvious one would be to be able to measure how many people consume different shows etc.
If you read their articles or listen to their shows on third-party feeds, they have no way of knowing. Before you claim this is a good thing, some show you love might get cut because they don't know it's actually popular.
I just use their apps, so I'm not affected. I can see how people who prefer aggregate apps would dislike this, however.