HN adopted an anti-blockchain stance for the same reason it adopted a stance against memes, political ideologues trying to "red pill" people, culture war flame wars, etc.: to save itself. If it hadn't it would have devolved during the 2017 cryptocurrency mania into one of those abandoned forums full of nothing but spammy looking posts shilling cOinZ.

This is still a somewhat interesting place because topics that attract hordes of spammers and shills and low-effort memers are either outright banned or downvoted instantly to oblivion.