Kerf, I see exactly what you are getting at and perhaps this is something akin to some archers hating compounds.
I know people in archery who will have nothing to do with them. It's as if they wish they didn't exist.
Some of this is brought on by fear of the unknown; they know nothing about them so dismiss them so they don't have to accept that their knowledge is limited.
I see far more similarities than differences between longbow, recurve and compound bows and how they are shot. The differences are details; the similarities are the building blocks of all shooting forms.
Tiller is understood by Oly coaches, I suspect. What the differences are when shooting barebow and string walking is just an extension of that understanding. If the initial understanding is limited to a stated tiller difference of say 3mm because that is all they know and want to know, then I suspect they are not too willing to accept change. I know archers who still talk about string contact being "centre of nose and chin" . No variations allowed!
I go back to what I said perviously, how much extra does the coach need to learn, in order to coach barebow? My guess is that it is not that much; but it is enough to require some expert input and some willingness to learn.
I have posted enough times in barebow section to have some knowledge of sting walking and face walking and tillering for such. I am not as confident about what I know in those things, but there are plenty on here who could help me out I am sure.
Longbow archers use gap shooting and ground markers, so many clubs have access to people who understand that.
Tillering for barebow string walkers has been mentioned on here many times. There will be a not too complicated rule of thumb that could be written down to help archers and coaches alike.
We have had a real upsurge in the popularity of barebow and longbow archery where I shoot. I have updated myself to be able to help them out when they need help. It hasn't been difficult, AND I am not belittling barebow archers when I say say that. I am sure there are more things I need to learn.... but that is normal; and to be expected.