It's an open source textbook so professors will tweak it to suit the course they specifically want to teach. There may be parts of it that they aren't fans of o

It's an open source textbook so professors will tweak it to suit the course they specifically want to teach. There may be parts of it that they aren't fans of or would prefer to be done a different way so they can make those changes they want and share the ebook with their class. Ideally more classes would be able to do stuff like this but given the fairly "fixed"/closed source nature of most textbooks, this isn't really an option for most professors or courses.