It’s simply impossible to account for all the corner cases, especially when you have to factor in manual drivers who can behave arbitrarily (what if they purposely drive weird just to mess with the autonomous cars?).
In fact, autonomous cars may increase danger rates as human drivers become quite peeved at sharing the road with them, and try to derail them at all cost.
Maybe these are the reasons they gave up.
I got a car about 6 months ago with Level 2 Autonomy and I'd say it's even more than just trying to mess with them. Now that I know the subtleties of how my car behaves, it's easy to spot other drivers who have theirs engaged too. I can use that to my advantage when appropriate and it takes some ethics not to abuse them. For example, if I have to merge I'll merge in front of one of those cars, purely from a safety standpoint -- I know that car is going to respond and give itself lots of space. Of course, people could use that much more maliciously to take advantage of those cars "niceness".
I've never had anyone mess with my car just for the sake of it, but you can see the seasoned Tesla owners taking the opportunities that they spot. It changes the way other drivers drive if they can identify the behavior.
The scale of autonomous has been misleading. Either something is autonomous or it isn't. 'Level x' autonomy is marketing speak.
I am quite happy with incremental improvements in driving aids, e.g. how Intel MobilEye is advertised. Spaceboy Elon sold it all to us as an impossible future. I reckon that Apple probably got on board the electric autonomous driving bandwagon but can't perform the required magic. You can hire all the engineers you want to build magic things but after a while there is no point paying them if the magic is not going to happen. They may well have pivoted to a car type of thing that has great UX instead of 'magic'.