Learning requires metacognition. When learning something new from a text, readers must constantly ask themselves: did I understand that? what questions can I ask myself to check my understanding? should I reread that passage? should I consult a reference for background on that? etc.
In other words, readers have to run their own feedback loops. When readers are focused on challenging object-level material, they may not be able to effectively perform this kind of metacognition; conversely, too much effort spent on evaluation, planning, and executive control may make it difficult to engage with difficult object-level material.
The situation is perhaps slightly worse in video formats. In books, readers are in complete control of the pace, but in videos, there’s a default pace, and viewers must actively decide to subvert it.
My theory as to why this is true: Metacognitive supports require dynamic, participatory environments.
Matuschak, A. (2019). Why books don’t work. Retrieved from https://andymatuschak.org/books