Not only that, but here you're talking about increasing the cost of advertising exponentially.
The closest thing we have to what's being described here is a video game. 3D game development is one of the most difficult and unforgiving branches of software development.
To achieve what is being talked about here, BMW is going to have to hire a team of 3D artists, animators and programmers to realize this asset. And someone is going to have to make sure this asset performs well, and interacts appropriately with the world, and with all the other assets which have been created by independent and unrelated teams. Part of that is, driving around in this car can't use too much CPU and GPU budget so that it brings the framerate to a halt when it appears on screen with any combination of the infinite number of combinations of things which could exist in this world.
This stuff takes years and is hard to get right for mature AAA studios with decades of experience. The idea that every company with an ad department is going to get into this vastly expensive and unproven business is a dream for facebook but a nightmare for everyone else.