So why then have you registered with HN? ;)
Even with registration, the biggest task remains to moderate all user-generated content. Hence, imo, a bit of a barrier in first place is justified.
After viewing content and comments on HN without a required registration, they developed a habit of visiting and eventually found value in participating and created an account to do so.
With the current approach for the Problem Platform nobody can view the content or comments without a required registration, so prospective viewers don't see value demonstrated and will never convince themselves that adding yet another account to their digital footprint is worthwhile.
lol, I'm on noprocrast mode so HN actually blocks read if I've been logged in long enough. Of course, my brain works around that by reading it on incognito mode. But it's still useful as I spend less time writing.