If they don't care about Fediverse they wouldn't join it in the first place. It isn't just meaningless but actually harmful - people can gain access to the content on their service without being subject to their extensive surveillance and ads. Add to this all the regular problems with federation.

As for Google and XMPP, back in the days it was happening Google were playing good guys - they had infamous "don't be evil" motto, supported various open standards and open-source projects (they still do so to some extend of course). I think for them it wasn't really an intent to 'kill' XMPP, it just XMPP was too dependant on google so they suffered a lot when the company decided to stop federation.