Responsible teachers must plan their incidental photocopying further in advance than their book orders. Finally, it requires teachers to pay whatever fee the publisher names or do without. Some publishers ask nothing, some charge a flat fee per page, some take the class enrollment into account, some frankly gouge. These three rules deeply limit a teacher's flexibility to offer just the right fragments on a certain topic, and the ultimate losers are students. This is pious hypocrisy.
Authors make a pittance compared to publishers.
Those authors who make good money are rarely the ones whose texts teachers wish to photocopy for classroom use. Authors virtually never see a penny of the fees paid by schools for permission to photocopy their works. Publishers would improve their credibility if they would honestly admit that they are out to protect their own profits, not those of authors. I am an author, specifically an academic author. I write to be read, not to make a profit.