This is a really good case study in how difficult it is to find a balance between co-branding and maintaining a consistently high-quality design system across co-branding partners. There's a massive amount of work across UI/UX design and implementation done at Apple that assumes that widgets are not only using a serif font, but a specific serif font with specific kerning; that color-primary-60 and color-primary-50 and color-for-text-on-top-of-primary-60 are distinguished in a very specific way.
(Light/dark mode and localization efforts force a degree of flexibility here, but there are still a finite set of QA targets if you focus on primary language markets.)
But what happens if multiple partners want their own primary color and font? This suddenly has far-reaching, costly ramifications across multiple organizations. Even having planned your APIs from day one around color and style customizability doesn't guarantee that this can be done successfully. Taken to an extreme, frontend engineers (not just their embedded designers) are practically required to hold the context of all future potential customization needs in mind when implementing a component - a nigh impossible ask.
Which is to say that there are few companies that could pull off what the OP posits that car manufacturers are requesting, having a world-class interface that is customized to their brand. That's a tall order even for Apple's depth of talent.
What would make the map more fun to explore, and what other data would you like to see?