0). Anyone who doesn't speak English very well falls out at once. But that's probably the least of the problems.
1). I am among those who are much better at understanding written text. There may not be many of us, but we are there.
2). If a point is not very clear, it's much easier to go back to it in the written text, than to look in the slow YouTube. As an option, you can download a video, but… this simple action is obstructed for some reason.