Well, this is only a guess, but this is how I'd do it if I were running the business -

Renting to foreigners brings a whole host of new risks to rental companies. It's much more difficult to sue and collect in the case of a lost/stolen/damaged car/other claim, for instance.

Hence, to compensate the rental agency for taking on that greater risk, they need to charge higher rates.

Like I say, that's what I'd do, I don't know if that's the actual reason.

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