Your CPU's L4 cache is normally DRAM, and it's cheaper to shove some RAM into a microprocessor than to have a separate chip.

I simply refuse to believe the cost difference between a CPU with hundreds of megs of DRAM is cheap enough to be an appealing choice over the same chip with a gig of RAM. We're not talking about a disposable vape with 3kb of RAM, this is a car that needs to power a camera and sensors and satellite radio and matrix headlights or whatever. If it's got gigahertz of compute, there's no reason it's still got RAM sized for a computer from 30 years ago.