[barry-cotter]

Most industry's training materials are written by academics. Those academics who take the time to write textbooks probably do it because they want to use a good textbook that teaches what they want taught, the way they want it taught. In most cases there isn't really any other very good reason to write the book. Writing textbooks takes time away from something your tenure committee cares about, articles. And most textbooks sink into obscurity, pretty much without trace. It's lucrative if you get a blockbuster but that's not something to be terribly confident about.

Training materials for less academically demanding occupations are correspondingly less demanding to write. Step by step instructions aren't that hard. Instructional videos are expensive to make but YouTube has shown that people are even willing to do those for (next to) nothing. People really enjoy sharing their expertise on things they're passionate about.