There's a very easy solution to this problem, which ironically screws over the publishers far worse than general piracy ever could.
Any textbooks a lecturer requires their students to have should be paid for by the educational institution itself, not the students, for the institution to collect back from students at the end of each semester. The educational institution should purchase enough books to cater for the course modules, plus three, with one being destroyed in the name of producing a fully digitized (imaged and OCR'd) version, the other two are for the library to use as reference books.
When 'new editions' come out, said institution purchases just three copies, destroys/digitizes one of them to scan for the differences, and then either library subject matter experts or lecturers themselves annotate relevant updates for the set given to students (thus avoiding copyright infringement, but keeping the information fully up to date). The two reference books allow for students to have access to the unmodified copy for (you guessed it) formal referencing, should they need to. Any older editions previously kept for reference can also then be annotated and made available to borrow in the library, gradually building up excess stock as needed. As the changes between 'new editions' are often incredibly minor, and because many institutions are likely to be using the same books, this would very quickly become a collaborative editing effort.
When the stupid price gouged 'new editions' with minor changes stop being produced, and lecturers are finally forced to move on to completely different textbooks with completely different layouts, the glut of old books would then be donated to libraries around the country, along with the independent annotations, which can then be used to update any older editions in circulation.
As lecturers will always prefer consistency over rapid, major changes every year, constantly changing book layouts between editions would not counteract this approach, nor would discontinuing books faster (lecturers might even start adding inserts and otherwise "making do"). Even if publishers tried to charge more per book, that would just result in fewer sales to the people who would prefer having their own copy to keep beyond the semester, further harming profits. Instead, they would be forced to lower prices with the hopes that both the educational institution and students alike would start to regularly buy new copies again.