Textbooks have more features than they used to, like online homework and the like. The online component makes it easier for companies to push new versions. Professors are overworked, and intro classes, where book prices/versions rule the most, are massive. The dept probably doesn’t have funds for a full TA so grading becomes a massive undertaking. It isn’t possible in many cases to manage lecture halls without the features from the textbook publisher. So what is a young faculty member likely to do? Pick a text from a major publisher. Generally speaking, faculty aren’t out to get you, they are trying to teach you.