The cars are much more sophisticated and much more expensive than Nascar. But not faster......much less power. And of course all the tracks are road courses. Having only two makes reduces the interest somewhat, but worldwide it is still probably the most popular touring car series. The cost of those cars is just incredible....over $1mil per car less engine and trans !!
Cadillac doesn't sell enough cars in Germany to homologate the brand for that series. But that would be an awesome idea. There is no way to justify the expense of racing in that particular series. There are other series they could be in but the DTM is the ultimate and well regarded everywhere but here. They race all over Europe and now in Asia but the cars and rules are too dissimiliar to ours. They also have drivers from all over the world. That series is on satellite TV worldwide.