Guess I should read my own post then

Yep, the transition away from exactly this was mentioned in a lecture. We were told that nowadays (big) companies assume that their internal networks are compromised and run encryption + authentication inside between every host. Defense-in-depth at its finest.

Even parts inside a car no longer necessarily trust each other. They assume a wire tap everywhere. I guess it's also related how more and more features in a car are locked via software. So they are becoming more and more of a target for hacks. The endless cat and mouse game.