My impression is that HN readers are allowed to downvote something for any reason, including feeling like a topic is annoying or won't make for a good HN discussion.

So there's probably nothing more centralized at work than a bunch of readers deciding that they found the topic annoying or likely to be unproductive.

Of course, it can be hard to distinguish the results from a perception of people protecting their idols from scrutiny. But I'm not sure if anything can be done about that.