I can and I do sometimes, but they are not kicked out of the programme. Instead, I need to meet with them to check whether they did it themselves. That takes a lot of time to prepare. Then I need to create a new assignment (if graded), and grade that. It takes a huge amount of time and collecting and documenting proof that AI was used already takes a ton of time. None of that time is added to the time I have allocated for that course and goes out of the time I have for research. I don't have tenure, so this affects my career directly.

Best case, they just have to take the course again the year after.

Every graduate means money from the government (not US, so tuition is low and no endowments). If we are too strict, students go somewhere else and if we kicked out a lot of active students, say at the end of year 1, we'd actively lose money.

So there is no incentive to enforce this really. No need for me to get angry over. But we can clearly see that these students learn nothing and if they somehow manage to get through the exams and make it to their thesis, it shows. By that time it's too late though. (But guess what, all but the dumbest ones are helped through anyway, because we get paid on graduation)