Departments do do that - usually because they are short of funds and the money raised is used to fund consumables for lab classes. The university cannot raise a surcharge for certain classes, but they can sell equipment (read: course workbook) for that class. It's iffy, but still on this side of fine, no one makes a profit of it.

There is no excuse, though, for having to sign up for an account with a commercial publisher for exercises that are a part of your grade in that class. Normally you would pay a bunch of TAs to administer and grade the tests, but the university is too short of funds for that. So they outsource the grading to a commercial entity.