In the 1990s, plenty of people felt obligated to drive to the mall, walk into B Dalton, and purchase a 300 page book to learn how to use their new software. There was a whole section for it.
Today, they can find the equivalent information for free without leaving the device where the software is running.
Hard to say though if those books were in fact published by opportunists that surmised (correctly) that there was an audience out there that were either intimidated by the software manual (or assumed they would be without actually trying to read it) or who had pirated the software and so had no manual.
Today, they can find the equivalent information for free without leaving the device where the software is running.