We must use chat very differently, because I don't understand this.
The number of times I've found answers to problems ("How do I X? Why can't I get Z to work with vagrant?" etc) by searching through Slack channels, or viewing pinned messages that explained something (or had a workaround/fix for a problem) is huge. This has been especially helpful when joining a team, where searching the archives can be the first step in finding answers.
A lot of what we chat about could safely be ephemeral, but there's a significant amount of company / team knowledge which can be searched (or pinned). The friction necessary to have people put answers in Confluence (or similar) is high enough that often the answers (or discussions around them) are either never written, or not updated later.