Because the statement was one of fact, not opinion and therefore no correlation to ones' employer or experience as such.
If the statement was, "I think AMP for Email is perfectly fine as is and doesn't need an option to disable." that might be something to call for disclosure.
Does the person in question work on AMP for gmail? Also, I'm still uncertain that statements of fact (not opinion) necessitate disclosure in this case.
cramforce's position is quite Google-able (or DuckDuckGo-able). There are at least three other Googlers who work on AMP in this thread, and one other Googler who might or might not have AMP involvement (a DevRel). Only one discloses on their profile that fact, and none of them disclosed on their actual comments. They're not really hiding, mind you, and if you read a lot of corporatespeak, they stand out pretty well.
(toomuchtodo is indeed accurate that the Google Cloud team are top notch on disclosures.)