Lots of people have fought and died in wars over the belief that a book was the literal Word of God, and some of those wars lasted a lifetime.
Literacy is not required.
Watching video is far more engaging and entrancing than reading books to most people.
Video can be broadcast and consumed by huge numbers of people _much_ faster than written text.
Unless someone is reading text out loud, the people around them aren't influenced.
In court, especially the court of public opinion, video is currently infallible.