When I taught an electrical engineering class, the prof with whom I shared a syllabus and exams, made the exam problems look a lot like the homework problems. The kids who (probably) cheated on their homework lessons paid for it on the exams.
Perhaps likewise for the humanities courses. In my own experience, writing essays and term papers for the regular course assignments was what got me so I could write a decent essay quickly during a "blue book" exam. I don't know any way other than sheer physical practice, to learn how to do that. You can't pay someone else to practice for you.
I've caught a few people cheating, but I usually fail them for the assignment instead of the class and spend extra time working with them to get their grades up. I've only had one repeat offender and I enforced the rule. The student came up to me a few months later and thanked me. Said it made him re-evaluate his commitment to school.
My mom is a retired high school teacher, and it's a completely different story. Among the "perks" in her contract were legal representation and liability coverage.
When I was an undergrad, certain ethnic groups were untouchable on the campus. There was also a lot of paperwork involved and cracking down on cheaters would focus attention on the department.
A substantial fraction of contract cheaters (as in, the ones actually doing the work), are current or former adjuncts who need the money.