There are two types of college degrees. One is art, and the other is science. Artist are creators, and scientist study creation. Does an artist ever stop creating? I don't think so. They look at a style, and how many variations will they come up with? To a certain extent patterns get in the way. So, they are not just making shirts. The shirts are about some parts of life that they put together. Music isn't about a bunch of notes or words. It's about why. Perhaps all music is mathematical, but it is not created by math. It is created about life, as is clothes.
"But surely apprentices and journeymen learned to cut from just such books. It's a textbook, not just a "bunch of hints". Journeymen should be beyond textbook. An update on modern thinking. Beginners know nothing. They have to start somewhere. Take, for example, learning how to write literature. You learn some words and grammar. Hints on methods of setting up the story, which maybe an outline for direction and chapters. But you are really on your own. Your thinking is really about mass-production, which is far from custom. Custom needs a whole different model.