You are standing there, in the classroom; two dozen eyes are sleepy from an evening of gaming, chatting, living. But you are there, and you are demanding their attention. You are laying claim to precious teenage minutes, and I dare you to waste them. A minutes inattention in a teacher can loose a class, make them lose track, and spin back from hard won miles of slog through a hormonal forest of competing ideas. What matters, the only thing that matters, is the presence you share, and what it is filled with.
So you do a good job, you bring them in - you increase understanding. And then, the test comes. What pupils don't understand is that the test is not only of them, but also of the teacher. What has the teacher managed to convey, inspire and cajole into the pupil? Usually, there are a few glimmers of gold, a few inspired thoughts. Most of it is simply average, and some of it is horrible. Nothing new, perhaps. But then you look closer, and you find the writing style of the book reflected in student assignments, and you shriek, because that horrible rag isn't worth it's own weight in paper.
The writing style is overly clear, and laborious. It puts in many little word, like this, only so that the hard words should be a little further apart, because that is important when writing such texts for such you people. Infuriating. Here are a few reasons why writing is a bad idea:
1: It is uninspired. Flat writing makes for a flat emotion, and memory works best on heightened emotion. Emotion is the brain's way of noting what is important, and the brain wants to remember things that are important. Soulless writing diminishes the soul
2: Putting filler words in a sentence to create "mental space" has the opposite effect. Especially in an early learning situation, when the learner is inexperienced at parsing information, spreading out the crucial nouns too far away from each other, makes them loose connection in a mental sense. Ideas seldom stand alone, they are to be related for a maximal understanding, be it in social science or literature. Classical writing style guides say, "put the noun and the verb close to each other in the sense", and with good reason. It is a best practice borne out of experience, and now, of cognitive science.
3: Learning happens through imitation. Badly written books give badly written tests. The syntax of sentences are the skeletons of the logic of the meaning - and I don't think I'm going to unpack that much further. If you don't know what it means as a writer, you have some studying to do. For the layperson; Word order is crucial to meaning. Bad word order hides the meaning of words that stand in a special relation. When students use this dilute form of writing, they are making the thinking process harder for themselves. Ideally, notes should be taken in haiku.
4: Final reason. Textbooks should reflect the passion of those who wrote them (unless they already do), and also current research and issues. You don't need to make it completely coherent or all-encompasing - it is the teacher's job to sow it all together, and also provide the additional material, or guidance to find that themselves.
Please make good textbooks. These are so bad, I'd rather not have any.