Forums can and do go down or get deleted, there’s nothing inherent to it that makes it stay any longer then discord messages.

You’re comparing apples to vegetables here. Sure, forums can go down, but not all of them do. Take Reddit, it’s been around a long time and many people use it for troubleshooting. As for discoverability, a lot of the time when I do a web search for a problem, it points to one or more discussions on Reddit. And that’s just one example.