That's the good old Pareto principle for you: the last few percent are going to take a lot more effort than the first 95%.

More to the point, this falls into the category of safety-critical systems, with the added wrinkle of potentially being used daily by millions of people. Unlike many domains where software is applied, 80% of the way there doesn't cut it, nor does 95% or 99% or even 99.9%.

(Leaving aside the fact that, for all of us not actively engaged in autonomous vehicle R&D, we likely have absolutely no idea how close we are to success here, or even what all the relevant goalposts would be.)

Remember that we've been at that level with voice recognition since the end of the last millennium.

Possibly for driving in cities and highways on clear days, but we are nowhere close to having autonomous vehicles even match human drivers in 100% of possible/likely driving circumstances and road/weather conditions. That last few percent is the highest hurdle.

more like 0.1% there in terms of the work required to launch