> it does not have to be flawless, it just has to statistically cause fewer accidents per kilometer/year than what human drivers cause in a similar situation (which is already non-zero, and in some countries actually quite high).

Even though it logically makes sense, there are some nuances to it, most prominent of which is: When human drivers cause accidents, they are held responsible by the legal system. Who's responsible when your car made the decision? Is it Tesla? Is it the driver? Society is probably not going to accept a small improvement over humans while all the legal burden goes up in the air. It may demand a much higher improvement to compensate.