BMW does not race in DTM because those cars have nothing in common with the road cars unlike WTCC. And they are not the cutting edge of technology either, like F1. I cannot see Nascar being any different than DTM from BMW's point of view.
BMW is in F1 with the BMW/Sauber and formerly in prototype endurance in the IMSA/ALMS LMP1 class. Exotic cars to say the least and very, very expensive. The E30 M3 is a legendary DTM car. I think it has more to do with the initials than anything else. "D" as opposed to "W". DTM is a strictly German series. Actually BMW sells as many cars in the US as it does in Germany.
The point of the article referenced in my original post is that Nascar is a lot more sophisticated from a technology standpoint than most people are capable of even comprehending and that Toyota is following the money. Maybe BMW doesn't see much potential for growth in the American market considering the purchase price of it's models in their respective size classes. A Camry versus the 5 series is an approximate comparison. The BMW is twice the price. Maybe BMW figures that they are maxed out in the US so why bother spending more money to sell the same number of cars.