As other users have pointed out metrics is probably part of this but I suspect there's also a matter of music licensing. The Sounds app has more music documenta

As other users have pointed out metrics is probably part of this but I suspect there's also a matter of music licensing. The Sounds app has more music documentaries where they keep the music in (BBC podcasts tend to strip it out) as well as curated playlists of music. Securing licenses to broadcast copyrighted content on-line and in perpetuity has for a long while been a huge deal for the BBC and forms at least part of the reason why much of their huge back catalogue of TV and radio remains unavailable (source: I used to work there (caveat: ~7 years ago so this may be out of date)).