Actual learning requires you to think about what you just read, maybe re-read it multiple times, stop to try and solve a example problem, etc - all of which require you to stop/rewind which video inherently disfavors.

Besides, I think just like handwritten notes might have a slightly different neurological effect than typed ones, reading might just be a very different mental muscle more connected to comprehension; humans had oral language for much longer than any script, so maybe it came with some different connections to higher brain structures as well.