The Audi A6 comes in both a sedan and wagon (hatch back) variant (named "Avant"), I would assume saiya-jin was referring to the wagon variant. The only wagon variants sold in the US are the "allroad quattro" variant and the RS6 though.

Same for the 5-series, the Passat, and others mentioned. Those are available as wagons in Europe and still seem to sell well, based on what I see on the roads.

The Audi A6 Allroad is definitely a wagon. BMW had a 5-series wagon but stopped selling it in the US a little over a decade ago.

You are a bit lost and clearly no clue what you comment about, I personally have BMW 5 series wagon (F11 model to be precise). VW has Passat wagon, Skoda has Octavia/Superb wagon etc. I see them here in Europe much more often than sedans, if you go for big car you usually also want the maximum trunk space.