My guess is that the fine is either a slap on the wrist (so the house owner just chalks it up to business expense) or so sever that the house owner stops doing short-term rentals entirely. I've not used AirBNB, but I assume that the house owner doesn't really know anything about the renters most of the time.

One solution might be to pass the fine onto the renters, but that leads to another problem: "Quiet" renters would probably be more put off by the possibility of an extra surprise charge than "Party" renters. The latter category probably ignore the penalty clause when booking the apartment and then try to avoid paying the fine after the fact. So now your set of renters is mostly loud partiers and the problem is even worse.