Beleive me Jackson has not fallen out of disfavor. Even when I cannot find a copy in a college bookstore, I often ask to see what textbooks are currently being used in the physics curricula, at the graduate level. After consulting the book of orders, the bookstore staff invariably answers Jackson.
Forty years ago, getting Jackson was easy. All you had to do is go to your College bookstore with 25 dollars. I bought My copy of Jackson 2nd edition in 1976 for 25,00.
Up till about 15 years ago I knew 5 or 6 bookstores within 100 miles I could drive to that sold professional books in science math and medicine. Now I do not know any I have to go to MIT.Harvard COOP or Stanford. It has been about 10 years since I have visited them so for all I know, these place do not carry them and expect students to buy online.
Some regional college bookstores do not allow browsing. (This is why your kids cannot find a copy, also Jackson is probably used in only in colleges that carry a graduate physics program. In addition many college bookstores send books back as soon as the students buy them in the first few weeks in class). They probably should. I must have bought at least 1500 dollars a year on textbooks and computer software when books were more widely available. I knew about 10 professionals that did the same thing
Up until this post, I had the idea that any widely used textbook from Amazon would come within a week. I bet the bestselling worthless diet book or action video would come in 3 days.
I know how much my textbooks have contributed to my professional development. I actually fear for a future where nobody reads textbooks and may (or may not even) just read a limited section sufficient only to do assigned problems. I have seen some questions in the forum that asks, How important is it to read the textbook etc.
Consider the fact that many of our textbooks are available in (albeit, in paperback with poor paper quality) in developing countries at drastically reduced prices, Is it any wonder that students from developing countries generally get very high scores on admission tests in getting into US graduate programs?