Somewhat typical of academic volumes in recent years. The chief purchasers of these are libraries, mainly academic libraries, which publishers think are goldmines for them. Unfortunately library budgets are falling and more money is going to online and tech products instead of books. Recently Macmillan has imposed an embargo on their eBooks for libraries because they think they are losing money on the deal. https://www.publishersweekly.com/pw/by-topic/industry-news/libraries/article/80758-after-tor-experiment-macmillan-expands-embargo-on-library-e-books.html