I don't have to engage with every single person on HN to any extent just because I post on HN. I can also decide to engage with a post without having to commit to engaging with everything else that posters wants to add. I think it provides useful context if I clarify in advance WHY a follow-up might not receive a reply from me. In fact, most discussions on HN aren't back-and-forths between two people and arguably benefit from that.