"How hard can it be to make a car, especially a self-driving car?"
I remember interviewing for a position with a company that wanted to branch out into autonomous vehicles. I've worked in automotive, though not on anything directly related to building cars themselves, and I can tell you that building a car is something that takes decades to perfect. Some companies take some shortcuts and get to shipping vehicles in less than a decade but they should be treated as anomalies, not the norm.
Bully to Apple for making the attempt, but again, if you want to build a car expect it to take much, much longer than you realize.
"Apple Cancels Work on Electric Car"
https://apple.slashdot.org/story/24/02/27/195235/apple-cancels-work-on-electric-car