They do however use SoCs for HMI/head-units/carputers now however. The bigger reason is just the nature of automotive development. Every part is developed by a

They do however use SoCs for HMI/head-units/carputers now however. The bigger reason is just the nature of automotive development. Every part is developed by a specced or sourced by different teams and outsourced to a different Tier 1/2/3. Things are designed to be modular, so if you pick Option A for something, it might use ECU A, and if you pick Option B, they might pack a whole different ECU B. Also, every ECU is costed down to only support the intended application, so ECU A likely doesn't have the extra bandwidth to add on extra features for Option B. Also, none of this is decided or developed at the same time, so you have all the different features and ECUs developed throughout. Some things are changed mid program. Some things carry over from previous programs, so it's usually just easier to go your own way and not work with other teams on combining features. Every automotive OEM has a person who comes up with the brilliant and cost saving idea of combining ECUs. I know 4 such people from different OEMs but they have all failed for some of the reasons mentioned above.