We generally try to discourage the use of real-world branding within Automation in all aspects.

Beyond that, real-world auto manufacturer logos are copyrighted material, and technically would fall foul of the Steam Subscriber Agreement if someone were to upload them to the Workshop.

As for the fictional brands people have created over the years, the problem there is that in order for a mod to be uploaded to the Workshop it has to be "cooked" through the Automation SDK, which means you need the original model files. Trying to get all of these so that one mod would contain them all would be nothing short of a nightmare!