Because it was built by a GM subsidiary in Europe there wasn't any way it could ever been a volume model. Who knows what motivated GM to try to sell this (in the U.S.) thing to begin with.
Maybe the Outback? Flashbacks of the old GM where they tried to compete in every vehicle segment?
If you compare the two vehicles on paper on the specs that 95% of buyers
should care about for their actual usage, the TourX wins. And stealing half the Outback sales would be a 1/3 increase in total Buick sales... Also half the car enthusiast websites had an article every month lamenting the scarcity of wagons, maybe a marketing exec thought the time was right for people to actually buy a nice wagon? Nope.....
Probably this car helped cement the fact, for the domestics at least, that many of their vehicle buyers really just use their reptilian brain to buy cars... They feel comfortable when they are seen as tall(at a minimum, why tiny SUV's sell) ,big, flashy, powerful... Things like efficiency or driving enjoyment aren't going to sell a car, as those are harder to see and many of the buyers peers don't see or care about those at all.
Also the Buick brand is a non-starter for lots of people, its quasi luxury for old people? My wife would have needed lots of convincing to approve one, even if it was sold in Canada. Probably they should've made the TourX a Chevy and gone more "Outback" on it if they wanted to sell it as rugged and capable?, it was a proven formula at least. Cladding on a normal wagon doesn't really please anyone I think, to obvious its just for show.
Also maybe I think, lots of people want their social groups acceptable "Bro Dozer" truck? Something as big and flashy as you can afford to run, or be able to drive comfortably? A low sleek wagon, is more of difficult sell I guess.