To "work", as self-driving car has to be able to deal with all contingencies, such as unexpected heavy traffic, pedestrians, kids, drunk college students, sudden rain, sudden fog, constructions, police redirecting traffic, etc.
Oh, and it also shouldn't kill anyone more than once in 100 million miles or so. Even if some trips turned out to be slight less simple than predicted.
You edited your comment without any mention of it. This is considered bad etiquette and is derailing to the conversation. Please try not to do that in the future.
Clearly it does work for simple trips.