Not only written text is a faster way to communicate information, it is so because it has much bigger context window:

"A moment" in a video is exactly that, a moment of time, either a frame or a couple of seconds that will stay in short term memory.

"A moment" in a text is a page or two facing pages. There can be diagrams or formulas there. It is extremely easy to direct attention to parts of these pages, in any order.

In a video, "moments" in the above sense are generally low information, quickly changing in linear order. In a text, they are fewer and of higher density. It seems that the second type is easier to commit to long-term memory, to understand, etc.