Because they are the freakiest things ever.
But it is funny. Not because it’s German, just because you expect them to go around yelling “exterminate” and then you hear something along the lines of “exterminieran” and it’s so not funny but it really is.
And it’s like, stop laughing because people are dying and everyone is in danger and the very existence of the universe is being threatened.
But at the same time it’s like, what the heck kind of sound was that I have never heard a Dalek make a sound like that where did that even come from oh I see we are in Germany now, look at that, that would explain it.