[kayfox]

I think part of it is "it works for me" thinking in conveying information. Someone who is good at pure reading and writing may not think to add any illustration to their work, in fiction and some non-fiction that works, but sometimes it really helps visual thinkers if you include some pictures or diagrams to show what the thing is.

I spent a long time trying to figure out math until I encountered college texts that represented things geometrically, it probably had not occurred to those people who wrote the 20 year old math books I encountered in high school to do such things, but since then someone somewhere figured out how to help people learn better by conveying the information in additional forms.