I think you're the one who's demonstrating an atypical case here; most lectures aren't presenting on some rapidly changing topic, and even if they are, there is some Wikipedia text that is kept up to date.

>The main issue is that none of this is equivalent to the transcript. Nothing of what you propose would make the video accessible to a deaf person. A textbook chapter or the lecture materials are alternatives to the video, it helps making do without the video, but doesn't make accessible the part of video where the lecturer is writing something interesting on the blackboard and explaining something that you can't hear.

That's overstating it. The relevant metric is, if some deaf (or video-hating like me) person wants to learn the material, do they have a useful option? The fact that you can't make that specific video useful isn't relevant. Even pointing to some text that hits the same key points is major step up, and is trivial to do, and yet most refuse to do, just like most refuse to provide the one insight that they're making me watch a three minute video to hear.