Either rhetoric and discourse are unfamiliar to you (for instance, that a basic tenant is that one does not make a strong claim which acts as foundational evidence for their entire premise and then assume it to be taken as fact based on statement alone -- if that were true then 3rd graders would win all arguments by saying 'nuh-uh'), or you don't understand that responsibility can also apply to you in many cases.
There's an even deeper assumption here, too -- you kept referring to blameful postmortems as "accountability", which leads me to think that you might believe you can't have accountability without blaming and punishing individuals. If this is indeed an assumption you hold, you should question whether it, too, is false.
The fun part is, my existence isn't necessary for you to do this, so your personal preferences regarding my tone and style won't affect your introspection and the resulting answers! :)
Usually when you don't know something, you ask someone who knows. Since you sort-of asked here, I'll give you the answer:
Blameless postmortems lead to fewer failures, which is ostensibly the goal here. So what do you get from your idea of blameful ones? Feeling good about punishing someone, even though you're increasing failures by doing so?