In germany, what you call cheating isnt even considered cheating.
On homework, we openly collaborated and handed in near duplicates without trying to hide it. Some students would just copy the work of others. None of this mattered. Nobody "went after" it. It just gets graded, you get your points and you move on.
Most people accept the fact that grades don't matter, but you need them for your resume. For some reason, universities have moved on from being institutions of knowledge-production to being diploma mills, and grades are their way of succumbing to societies need to make shit measurable. The way we cope with this is to just hand out grades that are utterly meaningless, but keep the system alive.
In the meantime, people carry on with their lives. Some people in university want to learn things, some are just enrolled because its a cheap livestyle choice.
In the end, nobody cares about grades. Whether I actually know my stuff is my problem. Not my professors. No company hires you based on your grades, but a lot of HR personnel will reject you based on them. So you need good grades. But good grades alone wont get you shit. We live in this weird limbo of grades being a necessity but beyond that, dont mean shit. They are the shittiest heuristic known to man.
If grades were a scientific theory, those who came up with them would be ostracized crackpots. Neither meaningful nor in any way falsifiable.
A written exam on quantum field theory can only test so many things. Since its written, you have to ask for things that can be produced in a given timeframe. That leaves you with memoizable calculations. Any professor will tell you that such an exam will tell you nothing about whether the student actually understands the subject matter. A 2 minute discussion of the topic in very high level terms is probably more useful to assess actual aptitude.
Professors KNOW that they cant possibly measure the ability of individuals in classes of more than 15 students. Why would they care about cheating? They are part of a system that doesnt make sense just as much as everyone else.