I'm wondering if music rights issues is why we haven't seen the 3rd and final season of The Flying Nun on DVD. I seem to recall Sally Field singing songs in some of those 3rd season episodes.
Not exactly sure about this but the episodes for this series might not be in the greatest of shape and would require a costly remaster which could be why the DVD plans were scrapped. There's a similar situation with The Farmer's Daughter TV series which would also require a costly remaster.