The problem is that smartphones had very little consumer uptake before the iPhone came out.
You had your Windows Mobile and Symbian devices, which were popular among hardcore turbonerds, but normies weren't interested in them. And that goes double for the US; there was more uptake of WinMo and Symbian in Europe, but very little in Apple's home market. The closest thing to a "normie" smartphone before the iPhone was BlackBerry, but most people who had one were business users who had their device issued and provisioned by their employer. And enthusiasts always pooh-poohed BlackBerries as "not a real smartphone" because it was basically just a messaging and groupware beast with limited general-purpose capabilities.
So there was a big gap to be filled. Enthusiasts had their market segment, business users had their market segment, but the ordinary consumers had nothing. And Apple gladly swooped in to fill this gap.
The problem is that cars are already ubiquitous, especially in the US. What can an iCar offer that a Toyota can't? Hell, even if you specify electric cars, other companies still have this covered. What can Apple offer that Tesla can't? And if you look internationally, it's even worse. You start selling electric cars outside the US market, you're going to end up going head-to-head with Chinese giants like BYD that are already kicking Tesla's ass outside the US.
The only real path forward for an iCar that does to cars what the iPhone did to phones is if Apple were to perfect true Level 5 self-driving. If they could actually pull off "Siri, take me to work", it would change things enough that normal cars would look like dumbphones compared to the iCar. But that's a pipe dream. Our roads are too chaotic for Level 5 to be feasible for a long, long time. In fact, I'm willing to bet that the reason this project lasted a whole decade was because Apple was throwing everything they had at Level 5 self-driving, and they canned it because after an entire decade they still couldn't make it work.