> book publishers to milk students with single-access codes and never-ending "new" editions to their books,

The best example of this is James Stewart's Calculus textbooks. It is priced so high and made him so much money that he built a $24 million "Integral House"!

Where the money from your Stewart calculus book goes - https://www.mprnews.org/story/2011/04/18/where-the-money-fro...

The House That Calculus Built - https://www.fastcompany.com/3052267/the-house-that-calculus-...

PS: Just to be clear, the above has got nothing to do with mathematicians and their work. It just goes to show how bad the textbook publishing industry is in shafting students that you can make money off of them by selling centuries old well-known mathematics.