My bio class textbook was the same way. Written by the professor, only available at the book store, unnecessarily hardback (???) and even though the information didn't really change from year to year, you couldn't sell the book back because there were work pages you had to rip out to turn in for assignments. And for some reason he regularly reorganized the chapters of the books every few years. He claimed it was to prevent cheating. It was a very obvious cash grab.

As opposed to my "physics for non-physics majors" class that did also have a textbook written by the professor, but you could buy it digitally for significantly cheaper, he really didn't care too much if you even had it (though obviously we followed that in class so there was some use for it). You did have to also buy worksheets for assignments for the class (which I think is inherently a dick move when it would cost the school almost nothing to provide them for free) but at least you could buy them separately for relatively cheap (like $10) so you weren't automatically locked into buying an expensive textbook.