Cannot see group in device list help

I don't know Spotify Connect and Google Home well enough to be sure of this but my guess is that Spotify picks up the current semi permanent grouping arrangement, not an abstractly defined list of rooms, which is all that Sonos user defined groups are. 

I think this goes a long way in explaining why you have brought some preconceptions to this that don't apply to Sonos. 

Let me illustrate how user-defined groups (UDGs) work. To the best of my knowledge (which is admittedly far short of perfect), here is the only application of UDGs in Sonos. Here is part of my system.  ‘Lounge’ is a UDG that I have just created for this illustration.  It is defined as Living Room + Dining Room.   The screenshot timings are out of order because I failed to take a shot I needed.  You can easily illustrate the behaviour for yourselves.

Start with just the Arc selected to play 

Then tap ‘Lounge’

Wow! It has saved me having to tap both Dining Room and Living Room!  I still don’t end up with the system playing on my UDG, because it doesn’t even deselect speakers that are not in the UDG but already selected. (I can deselect it manually.)

That’s it.  If you have a fifteen room Sonos system and often play 10 of them together it’s a useful facility.  But that is all it is - a facility to save button presses when creating temporary groups.  I think there is a sense in which you can say that UDGs don’t really exist.

So, for the avoidance of doubt, I am not saying that every concept of ‘group’ cannot be picked up by any app.  Just that Sonos UDGs are really just button press savers in the Sonos app. 

I could be off on this, but my understand of Google Home is that it is cloud based.  Meaning that when you connect to Google speakers, you are actually connecting through Google’s cloud servers, which maintains the list of devices and groups of devices that Spotify, or whatever service you’re using, can connect to.  So if you opt to connect to a group, the cloud server just translates that to play on the speakers in the group.

Sonos, on the other hand, doesn’t use a cloud server, at least not in this way.  Spotify connects to the specific speakers rather than a cloud server or any sort of central hub.  So, an entity or speaker that you connect to via API that actually is a group of speakers that doesn’t exists, is a different matter.  Where does the group definition reside exactly?  On every speaker in the system, on a central master speaker, only on the speakers that belong to the group?  I don’t know.  

There surely is some way that Sonos can revamp their API (causing 3rd party vendors to do the same) or completely change their control structure to make this feature available.  However, is it worth it?  I would not want them to work on this because it would take time away from other development efforts and it would surely introduce new bugs in the API that don’t exist today. 

This is absolutely infuriating that Sonos would market so heavily that “all products go together to create a perfect system” -- knowing that the majority of the planet uses Spotify, and that there is no way to play a Group from Spotify. 

I recently got a Roam and was happy to add it to my system but it does not pair to anything else, which seems like a borderline scam. It should be noted VERY OBVIOUSLY, “DOES NOT PAIR WITH ANY OTHER SONOS SPEAKERS.” 

It does group though. All speaker do create a perfect system, just not always from third party apps. Have you tried playing Spotify from the Sonos app?

Aswell as ‘grouping’ with any other Sonos ‘room’, as mentioned by @106rallye, a Roam will also happily ‘pair’ with another Sonos Roam, when both are on the same wireless connection.

Wish there was a way for third party apps to "see" these groupings, similar to how Google Home etc do it. Feel like that is the cleanest way to support any number of third party apps. For those apps, it's just a "speaker" and they don't need to know if it is one or a group (this is how Google home works). I personally feel like this is an important item for such a widely used and premium brand that is focused on ease of use for multi rooms systems. Spotify being a very widely used app and me not being able to play music in my entire house using the app (while I could do this with Google Home) seems like a major gap to me personally. 

I have started buying into the Sonos ecosystem, and this is the biggest issue I have faced, which has made me question if I made the right move. 

PS: in all the posts I read about these types of issues, I feel like some reply in an extremely defensive ways. I think we are not hating on anyone here, just asking questions and providing feedback. Let's all have an open mind.

As explained above this would mean a major rework of how Sonos does groups, just to serve people that do not use the Sonos app. I can see why this would be good for those people, but would it be good for Sonos spending developer time on this, while leaving other thing open (65k limit, limited language availability for SVC,  no Google Assistant on newer devices)?

The Spotify App on my iPad can deal with Sonos Groups.