Separate point to your question.
FB is under no obligation to provide more details than they need to because a small segment of the population (certainly relative to their 'customers') might find it interesting or helpful or entertaining. FB is a business. They can essentially do (and should be able to) do whatever they want. There is no requirement (and there should be no requirement) to provide the general public with more info than they want subject to any legal requirement. If the government wants more (and are entitled to more info) they can ask for it and FB can decide if they are required to comply.
FB is a business. Their customers are not the tech community looking to get educated and avoid issues themselves at their companies or (as mentioned) be entertained. And their customers (advertisers or users) can decide if they want to continue to patronize FB.
I always love on HN seeing 'hey where is the post mortem' as if it's some type of defacto requirement to air dirty laundry to others.
If I go to the store and there is not paper towels there I don't need to know why there are no towels and what the company will do going forward to prevent any errors that caused the lack of that product. I can decide to buy another brand or simply take steps to not have it be an issue.