I actually think there's a clear explanation for this: HN is much larger than it seems. There are millions of users. Every subgroup/tendency is going to be represented in a population sample that big, except for utterly obscure ones.
Which subgroups/tendencies show up in the comments is therefore more a question of the particular thread: the title, the topic, and the early comments. If it seems like "HN would be better than $X", that's only because we mostly manage to avoid the stimuli that produce $X responses.
Thinking that HN would be better than <insert any bad behavior here> is a bit too hopeful of an assumption. Everyone is prone to bad / ignorant behavior. HN users being no exception.
I disagree. Some communities are actually much better than others on a variety of issues. I mistakenly thought that this was an issue HN would have been better and more mature on too, but I'm learning I was wrong about that.
But compare your average 8chan poster to your average HN poster and you'll see that for sure not all online communities are the same.
I for sure never thought that all HN posters were free of hate/discrimination, I just thought they were better than we're seeing here. But I was proven wrong in that.
Which subgroups/tendencies show up in the comments is therefore more a question of the particular thread: the title, the topic, and the early comments. If it seems like "HN would be better than $X", that's only because we mostly manage to avoid the stimuli that produce $X responses.