Most people are just trying to get from A to B without any drama, the drama increases significantly as you approach 200. I suspect the median is closer to 160...
And then there is the construction that always put a crimp in things.
I've also lived all over the US. It's my general impression that the "typical" speed on unrestricted stretches of the autobahn and long, flat, rural, stretches of the US interstate system are roughly the same.
It's cool to see M5s and Fiat Alhambras (lol) zooming past at the rev limiter but most people get up to 85mph/136kph and chill out.
Germans love their campers so half the vehicles on the roads are towing caravans and going slowly anyways.