The reasons being: (1) I am horrible at editing and producing videos and that time I spend struggling could be time creating more written tutorials and (2) I'm not sure that people will really want / appreciate it yet. Many people (myself included) prefer text. You can't always be in a quiet place or have headphones on to listen, and reading a page at your own pace seems to be easier than video. But I am considering it, I'll do one or two and see what the feedback is for that.
Also, I found the discussion on this post[1] strikingly relevant in this context.
[1] - http://jaap.haitsma.org/2010/01/03/the-rise-of-video-tutoria...
I wouldn't mind an accompanying video though.
Not to mention that it also excludes deaf people unless manually transcribed, or if the speaker is clear enough that automatic transcription is possible, but I doubt that is possible with programming videos yet.
You can't search them for the thing you vaguely remember, you can't copy and paste code, you can scan them when they're too easy. You can't skip back and forth without loading delay.