What the fuck is wrong with those people and their fetish with Discord? It's not a forum, it's a fucking chat platform where you have to pay for fucking emojis!
I mean, the vast majority of interactions on any social media site aren't even conversations. They are Reactions. Someone posts anything about sexual assault or boats? Better make a reference to The Implication. Maybe someone will also realize what an incredibly obscure reference you are making and join in. And then you all have a laugh while someone talks about how amazing it is that people can have such a unique interaction in twelve different branches in the first page of that thread. And then they never interact again.
In that case? What difference is there if you are on a message board, a twiter, a twitch chat, or a discord?
What does suck is that people lose searchability. But that matters to a VERY small percentage of social media interactions.
They have closed off their community to outsiders. That's just sad, it's hard to add members if no one can see over the fence and ask about your community and then decide to join if they like it. It's not like they're giving away invites randomly also. That community will be like a hermit kingdom, all insular.