It’s not about assigning blame for the company writing the post-mortem. But it’s definitely about assigning blame for most people reading the post-mortem. Very few people read post-mortems for the sake of learning how to be better at release engineering and ops.
If I pay for your service, and you are transparent about mistakes and flaws, I will be more forgiving about mistakes and flaws in the future, and appreciate the work you do to fix them.
If I pay for your service, and the only communication is, "We know there is a problem, and we'll let you know when it's fixed", I may assume you are not equipped to thoroughly explain the problem, and therefore not well equipped to solve it.
The blame is already assigned. The users already know there is a problem. A post-mortem likely has a positive effect for the readers attitude toward the handling of the issue.
It’s more the people who don’t pay for the service, but might, that are quickest to see post-mortems in a negative light. The only reason they have for reading them is looking for justifications for culling the product/service from the list of contenders for when they ever have to evaluate solutions in that category.
In other words: post-mortems are good PR, but incredibly bad advertising.
And a world-wide outage followed by "we fixed it and trust us it won't happen again" is going to filter any service off of my list more so than "we had a single point of failure running in our CTO's basement and his cleaning lady pulled the plug. Trust us it won't happen again."
