So what do they have left that is adequate? Like around 100 tops? We aren't talking GTA5 npc driving ai here. It just looks like they are giving up on in car ai.
Performance aside, I suspect cost is also a factor. If you look at low cost PCs now, I can find mini PCs utilizing the aged Ryzen 2500U for a slight premium over one that uses an Intel Celeron/ Pentium Silver chip. The former while being the first gen Ryzen chip is still very fast when compared the the Celeron/Pentium parts, and with an iGPU that wipes the floor when compared to the cut down Intel UHD solution.
Cheap core mini pcs are at a price premium. Probably also is the case for a custom build like in a Tesla.
Concerning igpu, depends what you are talking about. For desktop image display and video playback Ryzen isn't significantly ahead of a 2w total system power soc atom igpu from 2014. But the Ryzen cpu would access files and start programs quicker and smoother, but maybe not first gen Ryzen. No need to limit it to 1st gen though. Ryzen's igpu advantage is only in gaming, which doesn't matter for those with dgpus or not gaming on an igpu. For infotainment display the new intel igpus probably beats anything Ampere, much less Radeon or AMD igpu. But AMD does have a relatively good gaming igpu for what that matters.
Atom has a power to performance ratio that's just too low for any modern application. A quad core Zen2 chip will blow it out of the water within the same power envelope.
AMD's RDNA2 is way ahead of whatever mobile chips provide (except Nvidia's Tegra, and that's debatable) - there's a reason Samsung wanted AMD to design their next iGPU. Heck, even Intel are still chasing after AMD's perf-per-watt in embedded! Remember Hades Canyon?
Atom has a high enough performance to power ratio to compete with ARM in phones, it just gets worse software support than windows mobile. Neither the Zenfone2 nor Leagoo T5c were lacking vs arm in perf/watt. The Leagoo had 8 cores and no heatsink. Just a bare black die and my daughter would still be using hers if she hadn't trashed the charge port. AMD isn't even on the same planet in that regard. Their I/O chiplet alone needs a fan.
Where Atom is lacking for light use is cache speed and memory latency. It is terrible and you can see the lag in lower powered parts. Ryzen over 15w doesn't have this problem. But neither does Core over 5w. Even Broadwell from 2015 (check reviews). Ryzen can win in "productivity" like cinebench, but this is an infotainment display.
How heavy of use do you think infotainment is?
Likely the Ryzens are good enough at the best price. Maybe Musk sees some Ryzen hype wave and is all about exploiting hype. Maybe both