Is the available content on all of these platforms limited in supply to Sonos?

I maybe can find an episode or two of a podcast, but can’t drill down into the full season list for example. And if I play them through my browser (directly in Spotify or BBC Sounds where I can find them) I can’t push them out to my Sonos system as Spotify itself will only seemingly find Bluetooth devices and BBC sounds doesn’t offer this at all.