I never understood why everyone moved to discord. Regardless of this, it actually just sucks and is hard to use. Discord really gives me hope that the fediverse will succeed, just because the UI sucks so fucking much.
Discord replacing the third is the saddest. It completely isn't fit for purpose. Part of the reason you can't find anything on Google now is that forums died, and Discord is unsearchable.
Discord just switches it's business model yearly to clone the one thing it hasn't killed yet. Started out to kill TS and IRC, then went on to kill the forum, then it tried to kill Steam/GOG but failed, now it's trying to kill Patreon.
Also, weirdly, a lot of people seem to use Discord for things used to be (and I would say should) be on a forum (or community, magazine, etc.)
Trying to follow the thread of a discussion about some obscure point you're interested in is much easier when it's in a thread, instead of an undifferentiated chat log with a bunch of unrelated cross-talk.
Exactly, I can go to discord and create a new server with a few clicks. Even as a somewhat tech savvy person I am not that confident about setting up a server, securing it properly, making it scalable for large amount of users, handling data storage and backups and all that.
Versus Slack, it was an easier sign-up process for ad hoc communities. You could just have people sign up instead of going through an approval process. (Slack's approval process could be automated with third-party tools, but it was a hack. Slack was meant to be a specific group of known people.)
It's definitely marketed that way, but I'm on a few Slacks that are just small, private groups. It's private by default while Discord is public by default.