The short version is that users flagged that one plus it set off the flamewar detector, and we didn't turn the penalties off because the post didn't contain significant new information (SNI), which is the test we apply (https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...). Current post does contain SNI so it's still high on HN's front page.
Why do we do it this way? Not to protect any organization (including YC itself, and certainly including OpenAI or any other BigCo), but simply to avoid repetition. Repetition is the opposite of intellectual curiosity (https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...), which is what we're hoping to optimize for (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...).
I hesitate to say "it's as simple as that" because HN is a complicated beast and there are always other factors, but...it's kind of as simple as that.