Shadowbanning could go away if people were actually ostracized, which means expelling from community. Currently if you ban someone, you only ban a single account and they can create another one. Some people are banned not because they don't know what they do, they are banned because they are intentional on destruction of society. They won't learn anything from banning them. That's where shadowbanning comes in, they can shitpost all they want, but rest of us doesn't have to listen to them.
This is still assuming good faith on the commenter's part—some people don't want to correct their behavior. Maybe they're doing it for money, or for attention, or maybe they just like annoying others.
And even if you are someone that might be willing to correct your behavior, it's not HN's responsibility to guide you to rehabilitation, when it comes at the cost of making the conversation worse for everyone else along the way.
It’s better to correct one’s behavior if one knows what the hell they are correcting. Correction and rehabilitation can’t have progress if you just put them in their own echo chamber.