I have trouble following someone else's pace in a video (or audio for that matter). I also like to be able to copy and paste code into my editor. Navigation to particular sub sections is easier too.
For me, hearing a description will often come with some emotional cues. Stuff like, "Now this is cool..." or "Oof, forgot the iterator..." help me learn where I should be paying attention.
Text often has a hard time conveying the same set of information. Sure, you can type 'watch out!' in a yellow box around some text, but my ape brain doesn't pick those up as the same as watching (or listening) to another ape brain make the mistake or exclaim in delight.
I think the video format is a kind of forcing function in terms of the presenter really explaining things (if they aren't just reading off the screen). Which in turn made the transcript great to read.