Agree 100%. Not the most important example, but I used to be heavily into World of Warcraft. The go-to place for discussion of high end play was a forum run by the guild "Elitist Jerks". Everything was there out in the open, to be read and indexed and discussed and preserved indefinitely. The forum eventually went away, but the info was still available thanks to the Wayback Machine.

Fast forward to 2020 when Blizzard put out WoW Classic (basically the original 2004 state of the game again, as a nostalgia trip). I was bummed to find that all discussion of the game had moved into discord servers. And not just one. There was a separate discord for every single class (mage, warrior, priest, etc). Sometimes more than one if the community couldn't agree on which was best. Every guild had their own discord. Special purpose servers existed for niche topics. If you wanted to find a piece of information, you had to hope that a helpful moderator had pinned it somewhere, or else rely on a crappy search feature. If a server is shut down or you get banned, all of that info is lost forever. It's a nightmare.

Discord is a perfectly good tool for real time chat. It is a TERRIBLE tool for summarizing and preserving knowledge. But unfortunately it's increasingly being used for that purpose and I do not for the life of me understand why.