What government is the one that should make those regulations? Would that country demand that special local license for anyone driving a car, that could technically go over the "fast" limit?
Or should every region just unify and force them? And how would this work exactly? Not all fast cars are as hard or easy to handle. And if that special drivers license would be issued in one area, it doesn't mean that they can drive that car as easily in different conditions in different countries.
You are right in sighting how it might be on the car if driving in another country, so actually a lot of fast cars are designed in different ways at which there are particular kind of roads that's suitable for it so when somebody use it differently from how it was meant to be it becomes another thing, sometimes bad road can affect the performance of such cars because since is mostly designed in a way that the lower side of the car is not far from the ground it doesn't need to be driving on a rough terrain roads, so actually so long as the car is on the market no government will restrict anybody from buying a fast car.