

As someone pointed out on the comment, one of the reason is Money, the other one is safety and security based on Vehicle manufacturer claim.
Yet, nobody can stop you to sniff and monitor your own car CAN/OBD2 interface using as simple as cheap microcontroller and compatible OBD2 interface kit (e.g CAN Transceiver/Controller kit).
EDIT: So far this curated list helpful to me for CAN bus based protocol.
Thanks for the link, this article is more clear compared to the posted above.
I’m more interested to the scope of the exploit whether it could touch the flash of the controller or not as you can also do OTA update through the BLE component.