I think you might want to reconsider. I'd note that the Orlando nightclub shootings were flagged[1]. This of course wasn't as bad as in Nice in terms of fatalities, but is somewhat comparable (insofar as that is possible. What a horrible thing to have to compare). Comments there seemed to try to imply it was some kind of conspiracy, but I think the behaviour there was exactly the same as with this attack. I think we are seeing fatigue over terror attacks - people are just numb to the tragedies and feel like discussing it is useless.
I'm not sure if you are French or lost people in Nice, but if you are you have my sympathy. I was in France only a few months back, and this event made me both sad and angry.
HN is certainly Silicon Valley centric, but that is expected given its origins and audience. However, my impression is that coverage of EU tech issues gets more coverage than most places. There is certainly more coverage of US politics than other places, but the majority of that is related to tech issues.
(I'm not from the US, Canada or UK, nor do I live in any of those places)
[1] https://news.ycombinator.com/item?id=11888228