> It always shocks me how low this number tends to be for highly skilled craftsmen.

Generally speaking (only a Sith deals in absolutes), engineers want to engineer.

There is no incentive for management to nudge the best performing engineers to teach their expertise in their craft[s]. A high-performing engineer "reflects good" on a manger. The way incentives are generally structured, this becomes a problem that perpetuates itself: Everyone in the management pipeline gets more money for the high performing engineer to keep engineering, rather than to teach.