That's a good point. These targeted funnels should exist. In fact, one existed from @jongolson, I forgot what that program was called.
There are some problems with onboarding+training funnels though. The only way to effectively do them is to build an email list and create a targeted email series. The problem with those is that they often go to spam or people purposely enter their email addresses they don't usually check. The other option is to create a website like Jon and Blain created years ago, that works step-by-step, promote it and get people to join, and from there, everything else that's in the funnel. I don't know of another way to create a funnel.
But that doesn't exclude the fact that each app should have their own internal funnel that leads the new user through the early experience with the app, after they join.