It makes sense when you consider that before Spotify, he/his team were having to chase down that money with no guarantee, subject to the whims of sponsors and audience and YouTube.
Now the money is guaranteed and they can just focus on the content in the show. Sounds like an amazing deal.
I think the effort is mostly around copystrikes. YouTube demonetizes and removes his videos whenever he plays even a snippet from a copyrighted work. If Spotify's lawyers handle those issues then Rogan can focus more on the show.