It’s happened in lockstep with the political radicalization and censorship across the internet, eg Twitter and YouTube.
Contrary to fluffy language, HN is a censorious community that uses downvotes and shadowbans to shape narratives.
Edit:
For overly literal readers — note, I’m commenting on rates not saying it never happened historically.
It went from being rare and limited to contentious topics to routinely finding quality replies buried for wronngthink.