All countries in Europe except Germany have a general speed limit, most around 80mph. Towing a trailer has even lower speed limits, for example in Germany the max legal speed while towing a trailer of any size is 50mph, even on the Autobahn.

This in combination with beefier rear frames on euro car models (and no truck sales this would cannibalize) results in a higher towing capacity rating. It is much more common to have a utility trailer for the 3-4 times a year you would need it.

In reality people go up to 60-65mph with a decent trailer, that is about 100km/h.