To be fair, a book is fundamentally a wear item. I remember learning how my university library had its own incinerator. After a certain point it makes no sense to have 30 copies of an outdated textbook taking up space in the racks. Same goes for beatup old fiction and what have you. One might think a little urban school or branch library might want some but they too deal with realities of shelf space constraints and would probably prefer that their patrons had materials more current or in better shape.

That being said, I’m sure these companies did not exclusively buy books at the end of their life.