The truth is, I just don't do much video and I don't know a lot about it. My wife does the video work but she's just a basic shooter. When I write books, I try to do them on things I'm fairly knowledgable about to avoid a situation like you had with the $100 book - I don't want someone buying something from me that isn't useful, insightful, and accurate. My skill set with video isn't even close on any of those three, at least not to a point where I'd publish a book about it.
In addition - and I know this is a little ironic - my field time is somewhat limited. I spent most of my time working on books or videos. When I am in the field, I enjoy shooting stills and trying to improve my images. I'd be sick if I missed a great still opportunity because I was shooting video. At least that's how I feel at the moment. In time, I may eventually start to enjoy video (I do play with it from time to time), but for now I'm a stills guy I guess