"The argument was that chat groups have become indispensable tools for students taking courses online during the pandemic. The essay detailed all of the useful info passed around in chats. I totally agreed with this point....Their strategy was to leave the chat before every quiz and midterm so that they couldn’t be there for the cheating. Then they rejoined afterward."
So, in order to be competitive in a class where (whether explicitly curved or not) the difficulty will be adjusted up or down until the "right" portion of students are passing, even a student who wanted to not cheat needed to be in the chat. He made a course in which it required extraordinary efforts to find a way to be able to both pass and not cheat, and then acted surprised that so many students cheated.
Any teacher who can fire up R to process the chat group logs, could have figured out a better system for quizzes and tests, so that it wasn't this hard to be competitive without cheating. Also, if he hasn't ever taken a course on game theory, he should; if he has, he shouldn't have passed.