> The towing numbers are always higher in Europe than US too, despite being the same cars (as far as I know).

Mostly due to differences in environment, AFAIK. Americans drive faster, and towing instability seems to increase with the square of the speed. Also, most travel trailers in the US wouldn't be car-towable anyway, because we have expectations on amenities and size that are predicated on using at least a half-ton pickup for the tow vehicle. Trailers with the compromises needed to be towed European-style aren't popular, so it becomes a self-reinforcing cycle.