Waymo spent a long time at about that level as well, and it's a common situation with AI: you can get 80% of the way there really quickly, and then that next 19% takes orders of magnitude longer, and the next 0.9% is even harder, etc (pretty much anyone who's ever tried to actually apply a neural net for anything will have encountered this). Self-driving cars need a level of reliability basically unheard of for AI or even a classical software system of similar complexity (there's more complex software systems, and systems with higher reliability, but the product on self-driving cars is extreme).
A liability-viable self-driving car needs to be reliable enough that you would expect to see zero significant errors in a typical journey. That's around the point where you will only have a few articles about one of your thousands of cars going wrong each month. Commercially viable needs better than that.