Many programs are willing to sacrifice having an excellent teacher in exchange for someone with a corps jacket. Every year many schools post an opening for the same position over and over...with the same desire for corps experience. While some of the turn over could be due to promotions, more likely the person was a complete bust as a teacher.
Are there good teachers with DCI experience? You bet! However it seems in my experience that for every one good one, there are five that aren't.