We used Slack and we had a Confluence Wiki. No one bothered to keep Confluence up-to-date because everyone was just used to ask ad-hoc questions on Slack and get an answer by one of the respective team members. We "solved" this issue at one company with one reasonably simple policy: people were free to ask questions on Slack as much as they wanted, but the response should always have a link to the related Confluence page. You could even answer the question directly with a TL;DR, but the Confluence Page link should always be part of the answer.
Every time that there was an Slack response without a link to Confluence, the responder's team would get a mark, and every month the team with the most marks would have to bring something to the rest of the company. Basically, it forced everyone in the team to step up their documentation game, and it got everyone in the spirit of "collaborative editing": sometimes, people would just write create a page with a very basic paragraph. Another team member would use that to extend the answer and so on. In just a few months, every department had a pretty solid documentation space and we even got used to start our questions with "I looked for X on Confluence and didn't find anything. Can someone tell me where I can find info about it?"
So, yes, you are right about the disconnect between "what experienced people want" and "what beginners want", but even in this case it would make sense if most project managers used real-time chat platforms only for initial inquiries and triage, but used this inflow to produce long-term content in a structured document or wiki.