Leverage only goes so far. Since it was originally a BBC show ~20 years ago, chances are that country-specific rights were sold off long before Netflix got involved.
It's likely impossible to say without having insider knowledge. Perhaps somebody with international IP law could weigh in.
But it appears there's an added wrinkle. Back when the show started production, MRC sold off rights in countries where Netflix didn't yet operate. CanalPlus in France and Sky Deutschland in Germany managed to get exclusive rights in their respective countries. Netflix is trying to get the rights globally, but they can't force anyone to sell them anything.
MRC licensed the name and concept from the BBC. That license would definitely not be regionalized.