If this is something you want to have a discussion of you'll need to ask yourself whether the problem is high level players not really wanting to put forward the time or whether there isn't a space for them to do so.
Tf2 Coaching Central has spaces for coaches to host classes, events, review sessions and post in a channel meant for guides and resources where people can search for key words for what they're looking for If they can't find an already existing guide in there. We're also working on converting the text channel to a forum with better organization and actual tags. Even though we don't allow high level players to play pugs, coaches can get an exception to just be med locked as well.
Wonder for instance found some of his favourite high level educational videos (both old and new) and posted them there and sometimes would pop in to answer text questions. A lot of high level players think they have to be a professor or bust.
I'm sure RGL is also planning on adding unto their guides section.
I've asked adv / invite players and outside of the Newbie Cup, the consensus is that they'd rather have people come to them than the other way around being fairly content with teaching a small subset of people in private. It would be great even if Invite players kept the same relationships but did it in a public discord so people can at least see a learning environment, perhaps even have people join muted to watch. There's a lecture hall channel explicitly for that purpose. A lot of coaches apply and then never do anything. I can't always blame them but that's the state currently.