Why do textbook publishers pump out a new textbook edition every few years, particularly for universities?

For profits? Legal obligations/restrictions?



Also, do you think I should make digital scans of each page of my calculus book and put it on my computer, and then post it on the internet for free download? It would help a lot of students with textbook prices/issues.Why do textbook publishers pump out a new textbook edition every few years, particularly for universities?
Publishers like to update and bring out new editions, so that students will buy them rather than re-using older editions.



By making digital scans of your calculus textbook, you would infringe copyright unless you have authorisation from the publisher or writer of the book. Yes it would help a lot of students who cannot afford textbooks, but copyright legislation exists to protect the works of the author.