> Why do employees at big tech names (FAANG et al.) are so often so cautious as to include this as a foreword everywhere?

This isn’t just ‘big tech’ - I work at a relatively small tech company, but I’d never want anything I say about the company to be mistaken as some sort of ‘official statement’ especially if it related to an incident that possibly had a financial impact on external parties, and could conceivably be misused in that context in the future.

I go as far as never writing private emails from my work mail for the same sort of reasons - although that is from a possibly over-abundance of caution.