Another thing (that the story goes into in depth) is that cheating creates a whole lot of extra work and stress for professors who would rather just be teaching material and not exerting enormous effort into policing other people's behavior and enforcing rules. (And that's really hard to do if you're afraid of making a mistake somewhere and punishing someone too harshly, or for something they didn't do.)

The students hunting for "the snitch" adds another layer of dysfunction. If someone joins the group chat and leaves because they notice other people cheating, then they could become targets of the other students. That's not the sort of college experience anyone wants to have.