I bet you it's because Spotify want to keep such features exclusively for Spotify Connect devices so choose not to provide the ability to Sonos whose approach is Sonos centric rather than Spotift centric (using Spotify Connect).
I moved to Napster near a year ago and haven't looked back.
"Customer centred" companies like Spotify that provide forum boards for the benefit of customers then constantly ignore (the responses don't have to be positive) questions just come across as arrogant..
Finally, Google has integrated its app with Sonos. Is disappointing to have to change of music supplier for a silly thing like that one, but I'm not going to change my sound system, and it's easy to cancel the Spotify premium subcription and get the Google PLay One (With three free months included!).
When you fully integrate Spotify with Sonos, I'll come back. I hope to see you soon.
I've been using Google Play for a couple of days now.
Initial conclusion - it's better than Spotify.
However the upgrade to the Sonos Contoller seems to have caused problems - Tunein Radio, which was 100% reliable now "stutters" sometimes, and it appears that you can only upload 500 tracks at a time to Google Pay -when I leave uploads running overnight (free bandwidth) it stalls at about 500 tracks, at about 03:30 a.m. BST.
I currently opened up a forum on the Sonos website to get Your Music added to the Sonos app so that our music collections could be played without any issues.
It is a real shame that Google Music has come in and seems to have wiped the floor clean from Spotify.
What I don't understand is that Spotify and Sonos are meant to have a 'close working relationship' with each other yet they don't seem to update their app to comply with new features that are launched.
The Sonos app is only just getting a much needed refresh from having been stale for years and even at this it's a very slow approach and wont allow the new features that Spotify has.
If anyone wants to take a look at the forum and perhaps voice their opinions then maybe we could at least get one party to acknowledge that things need done and we would like an answer.
I have been a Spotify subscriber for years and have promoted them heavily for years. Slowly starting to think Google is the way forward if I can use Sonos with no issues using them instead.
I feel like since Sonos wasn't on-board with Spotify Connect that soured the relationship a little bit. I really do wish that Sonos would make Spotify Connect an option if people wanted - I see it no different than the "cast" option they are providing for Google Music.