Perhaps they are also dealing with administration that says things like “The university insists that homework can't be optional”, as in the grandparent comment.
In any case, even if the uni insist on homework, the teacher can simply mark everyone who hands in their homework 100%. It is impossible for the administration to police it, or if they do, they'd need to hire someone to mark the homework (which conveniently solves the teacher's issue).
Students who copy all solutions from LLMs maybe learn something, but it's like 5% compared to what someone can learn by doing the assignment without external help, or even by asking their peers. It's a bit disheartening, because I invest quite some time and thought in designing the assignments.
It was very different before LLMs.