It’s a Google question. Sonos can’t implement the connection without Google’s lawyers allowing it. I’d recommend pinging Google directly, and ask them why they’re not allowing Sonos to do so. 

Right. Thanks for the information!

Is there a way to circumvent the problem?

Not that I’m aware of, and legally. There are potential illegal methods, but I’m not able to even confirm or not whether they would actually work, and I suspect were I to even discuss them here, it would be a violation of the community standards for this forum. 
 

As I said, your best bet is to petition Google directly, since they hold the ‘power’ in this situation. 

I have advised many people to change the country they are located in on the Sonos website (https://www.sonos.com/myaccount/user/profile/) to a country that is supported by Google, as this helped me when Google Assistant wasn’t available in the Netherlands. I’ve seen conflicting reports on the fact if this is still an option, but you could try it. GA is supported in the Netherlands now, but also in Germany and the UK.

The only issue is, there’s no guaranty that will work, either initially, as you point out, or long term. There are multiple ways for companies to confirm geo-location, and depending on the legal exposure, there’s always the chance that they’ll switch from one to another, or even use several simultaneously, which makes getting around the issue even more challenging. The lawyers tend to get nervous as people try to break the laws when using the services.