Sonos is bound by legal agreements, and can’t offer access until Amazon authorizes it. 
 

Here is the FAQ with the countries currently authorized. 

I believe it is Sonos that isn't investing in the server capability needed in/near India to allow for this integration to happen. Amazon isn't the party responsible for this Sonos decision.

I’m not quite sure what the ultimate benefit would be for Sonos to choose to block this. India is a large market, I would expect them to want to offer as many services as possible in order to increase hardware sales, which is where they make their real money. 

Unless you have some inside information to support the assumption….it just doesn’t make any business sense. 

It takes expense for Sonos to set up the necessary server infrastructure - it isn't a question of blocking it. Sonos simply does not see India as a target market which is why even sales into India are unsupported by Sonos - which I what Sonos told me even when I showed them that Amazon India was selling their kit locally. Not some random seller, but Amazon themselves.

So, buyers in India, buy at their own risk.

And yes, for this server thing, I do have inside information. It does not make business sense for Sonos to invest in the required server capability for a latency free integration with Amazon, who see India differently and have done their bit on the server side. I don't agree with the Sonos decision, but it is not a business decision for me to make.

For other India located users that may come by this thread, this is what Sonos Staff said here five months ago, and I doubt anything has changed since then:

As we do not sell products anywhere but on our own website, it seems Amazon have bought stock and decided to sell some of it in India (if it’s even Amazon that’s doing it - who is the seller?), and therefore it’s not our advertising or responsibility, but Amazon’s (or the reseller’s)