What are you actually asking? If you are asking why there are multiple microcontroller makes/models used in automotive electronics other than ARM architecture microcontrollers, then the answer is pretty basic. No single microcontroller make/model is the best at everything, cost, reliability, development time, so no single microcontroller make/model is going to completely control a market.
In case you don't know, ARM doesn't actually make microcontrollers. They design the core of the controller and license it to other companies to make, so ST, Atmel, Zilog, NXP, Luminary Micro... all make microcontrollers with ARM cores.