The more fragile presence of the information is actually a feature to some. If messages are more permanent and accessible, people can be more likely to stop and think before replying for more substantive discussion, instead of having a free-flowing conversation.

I generally also prefer forums that are searchable and public, but it's nice to have a real-time communication with someone over Discord (e.g. a couple sentences per message that gets responses, with some jokes sprinkled in). I think it's a lot easier to develop a one-to-one interaction or relationship with someone over Discord, versus forums structured like HN or Reddit.