Comment by nomilk
Exact same thought went through my head. Also note in the first few paragraphs they acknowledge the worst impacts to users. That's very selfless - often corporate postmortems downplay the impact, which frustrates users more. Incidentally, a critical service I use (Postmark) had an outage this week and I didn't even hear from them (I found out via a random twitter post). Shows the difference.
Presumably because Lichess is free thus doesn't have contractual obligations and SLAs that they'll be sued for breaching.