You gotta believe every brand outside Subaru has done their due diligence on that question and come up with the answer that it's more profitable to devote their resources to another crossover than to a wagon.
An interesting note on the Outback -- many recent reviews and best lists I've read make a point to say that it fits the modern definition of a crossover SUV better than the traditional definition of a wagon. I'm not sure if that's writers being more open-minded and literal about what you should actually be calling a "crossover," or if, just like the number crunchers in the auto makers' accounting departments, they know their article will get more hits if they put the car in that category.