Probably because car manufacturers haven't lobbied the relevant governments successfully. I suspect in many cases, the companies doing the copying are local and therefore have more influence over the relevant government than the foreign company that originated the design.

We also see a lot of cases where the copying isn't really copying. The first generation of Lexus IS300, for example was a compact rear wheel drive luxury sedan with an inline six engine and sporty handling. Most car people reading that description would immediately think "BMW 3-series", and that was, of course the best-known entry in market the IS300 was intended for. It's hardly a clone though; no component was directly copied from BMW, the styling was clearly not intended to be mistaken for a BMW product, the engine was already used in other Toyota products, etc....