Same as other instances of cheating? A lot of students copy from each other and don't get caught. If anything, LLM-isms seem a lot more obvious, especially if the students are trying to avoid thinking or doing work.
Anyway, I'm not a CS professor, so I'm just venting.
I’m not sure what you mean. Have a no-AI policy and fail those who ignore it. If students lie, discipline them appropriately for cheating.