Departments need to be helped to account by the student body. If your pricing is correct, and we are talking about a major 1st year class with 250 people, that's $57,500 for the privilege of issuing and marking assignments per session. For it to be saleable to departments I bet most assignments are already in the system and you just check off which one to issue.

It's academic laziness at the expense of the students. The uni makes more money by saving on the cost of tutors to mark assignments in those bulk classes whilst the students are charged more. Its a gross financial abrogation of responsibility for the welfare of their students.