I'm not sure it can be classed as a failure. Pivoted maybe, but failure? In what sense?
(Point is, the project might have been doing well and following the plans -- but Apple might have found that the target market niche was too small. Or the margins might have been too low for Apple.)
My point was that Apple probably cuts large projects with too little earning potential.
It is quite another endeavour to find $100K+ to buy a car, no matter how you can rationalise it. The total market size for car at that price is probably in the 6 digits cars worldwide and shrinking in the western world.
That falls quite far from Apple business model and expertise.
Because:
(1) it hasn't been done yet, nobody has a self driving car that is even close to being ready for the market
and
(2) just designing and manufacturing a new car is a huge undertaking.