HN just prefers the original title to avoid clickbait. The drawback is that sometimes context gets lost. On the bright side this sometimes will make you discover interesting articles which you wouldn't have checked out otherwise.

It provokes curiosity, I guess. It's like good ol' clickbait in that regard: ask a question with the promise of an answer, except the question is usually not explicit, just assumed by the user. Every time I see a contextless title I wonder "Hmm, what could this be about?" and click.