Firstly, I have to point out that Germans generally don’t fear sharks so much (there are no big sharks in oceans around Europe) – our boogeyman is the big bad wolf (sometimes even in form of a dog).
But media and air travel transported the enemy image of a shark pretty well.
Sharks represent our ingrained fears of the dark, the unknown, the water – the evil, indestructible, man-eating monster lurking in the depth to ambush every human who dares to go into or on the ocean.
Its big teeth, little eyes and absent neck are quite the contrary to the baby schema (cuteness) we find “cute” in humans and animals alike (first mentioned in Konrad Lorenz’ research, applied here to comic figures). That’s why we normally don’t fear
but the shark