The problem with everyone having moved from forums over to subreddits is that in order to interact with the community/ask qiuestions/whatever, you need to have a Reddit account and deal with Reddit's dark patterns, data collection and general disrespect for their users.
Compared to the current status quo of the likes such as Facebook, LinkedIn and Google, I think Reddit is relatively mild.
Also, keep in mind that HN is actually fairly similar a forum, and with that in mind, it’s very reasonable to point them into the direction of Reddit.