Every time a computer gets good at a task once thought to be outside of the realm of AI
Who ever said that?
Chess computers win by computing all the possible outcomes for a large number of moves ahead. The only limiting factor is computer speed. As computers get faster they can follow very similar algorithms aned get much better. At the base chess is not hard if you can calculate far enough in the future. People can not calculate far enough and therefore use other methods to win. By the way, we have had chess computers for 50 years.
The problem with real life is that it is not constrained by simple rules like chess. There are two many variables and too many situations that are non deterministic. For example, if you see a person standing near the curb. What do you think they might do. The prediction is based on many things; age, gender, which way they are facing, what they are doing, etc. They might just stand there or they might dart out into traffic. It is very hard for a computer to make predictions. The same goes for other vehicles.
Then something else will be "impossible" for a computer to do.
I never said impossible; just that driving a vehicle in the real world is very different than winning at chess. Compared to the real world chess is child's play. I don't think it will happen until our computing power increases by a few orders of magnitude. Never is a long time.
By the way, there is a big difference between a computer playing chess and a computer driving a vehicle. When a computer playing chess fails it loses a game. When a computer driving a vehicle fails people can die.