When I teach, I know I only have a relatively short time with my students. I want to teach them so much in my area of expertise, but there is only so much time.
Also, teaching teachers that our profession is one that must be committed to ongoing development, especially in the area of technology. There is no defined body of knowledge or skills that one can say, "Learn this and you've mastered educational technology." The field is shifting constantly and it can be a challenge, even for someone like me who is dedicated to the field, to keep up.