Well, because you can fail on initial assumptions. And may spread officially-false information.
This is not meaningless fluff. It may not provide info to technical persons, but valid info to other persons, as others noted (was hacked: yes/no).
Getting down to root cause takes time. It is usually multiple-things-at-once that caused X to happen. And then they must also make a decision on how to prevent X to happen again. All that must be written into RCA. It takes days not hours.
An example from my life: Service has intermittent disruptions. Antivirus activity correlated 100% with disruptions. Upon further investigation turns out that AV was just doing its job when there was less load. (And before anyone points out why on earth there is AV on such service, well, because it deals with user uploaded files)
So what should I have called out - AV is the guilty one? And then say: oh, no, false info.
Why? Why couldn't you just post that the RCA is still ongoing and that proper updates will follow? Otherwise all you get is meaningless fluff.