Granted, citations were needed for the post you're hammering. (I can't find anything online either way, re sleep loss in this accident.) But the author might not be speculating about the sleep loss, insiders sometimes comment here, in which case there won't be citations.
And this is why HN has the rules about "general news" it has.
Discussion of specific issues is interesting, but they're better discussed in extra threads instead of as speculations on a case nothing concrete is known about.
I haven't called anything "irrelevant". But without anything actually known, comments can basically only reiterate generic points about plane crashes or suggest random possible reasons, which predictably leads to discussions on how it's irresponsible to speculate or suggest specific (now dead) people misbehaved without evidence. It doesn't make for good content, and the fact alone that the crash happened isn't a good topic for HN.
This specific subthread starts with either speculation or unsourced claims of lack of sleep: That alone is an interesting topic of discussion, but better placed on a submission about a specific case where this is known to have been a factor, or some general article about it, not here.
My point is that we don't know whether the poster was speculating. I would be happy with a citations for all comments rule, but it's not in place now. The comment had details, wasn't general speculation.
That sleep loss contributes to accidents and is therefore relevant to the discussion (if true) is in no way speculative: https://www.ncbi.nlm.nih.gov/pubmed/?term=accident+sleep+los...