Except that in some cases, the automakers are not using a CPU with external interface hardware, they are using microcontrollers similar to the PIC series, examp

Except that in some cases, the automakers are not using a CPU with external interface hardware, they are using microcontrollers similar to the PIC series, example here: https://ww1.microchip.com/downloads/en/DeviceDoc/40300C.pdf https://ww1.microchip.com/downloads/en/DeviceDoc/40300C.pdf (Note, I'm not suggesting they use these exact chips, this is just an example of the level of onboard integration that is available for micro-controller chips). Single chip system, with built in analog comparators, timers, signal capture and PWM generation module, serial UART, etc. I.e., a whole "system on a chip" with the external world interfaces already built into the chip. Changing one of these for an ARM CPU with external analog comparators, timers, PWM modules, serial UART's, etc., is a redesign effort, not just a "change the chip" effort. If the clock speed possible via the internal clock oscillator is sufficient, then this chip needs only +5V and ground (plus programming) to be able to interface to and control some external analog or digital equipment.