Law school textbooks are among the worst when it comes to actual value. The majority of such books are typically known as "case books" because they simply contain abridged versions of legal opinions selected by the author(s). There is minimal interstitial text, usually a few pointless questions that are supposed to cause a law student to think about the legal implications in greater detail. These are routinely skipped when briefing the case and integrating the same into an outline for study before the one great test of the semester.
They are wholly useless books outside the confines of law school as the cases they present are abridged, and often times presented simply to show the historical development of the law. Selling them to other law students at the end of the course was the only way to recoup any sort of value from the texts at all. The promise of receiving a digital copy to keep at the end is meaningless because the value of the book is non-existent once the course concludes. And the publisher knows it, hoping the promise of a digital copy will forestall claims of first sale doctrine violation.
I had just two instructors who didn't buy into the law textbook scam. They provided us with a series of legal cites to cases and Code sections that we should review, knowing full well we could pull them off of Westlaw/Lexis Nexis (or, these days, Google Scholar) to review. Both of these instructors taught the most informative, interesting, and useful courses I had in all three years of law school, all without the extra $120 fee for a useless collection of partial cases. I wish more professors followed suit with these guys, who were both active lawyers and not full time professors.