Yes, there is: I am a touch-typist. So the layout of the keyboard is wired into my muscle-memory. Trying to switch layouts wrecks havoc with that. I tried it for a while, when I had to use an English layout at work, and it was very detrimental to my typing abilities. So I had to decide on one layout, and my native tongue won. As you see, I can type English text quite fine, just the brackets are more painful to type than parens.
How long did you try? Of course learning to touch type on a different layout will take some time but that doesn't make using brackets in programming languages unreasonable.
Using a German layout is very much a choice you have made and is no reason for you to demand that programming languages should make everyone else's life harder to acomodate those choices. Even for German text input, umlauts and sz are rare enough that it is not much of a hindrance to have to enter those via dead keys or compose sequences on a layout that doesn't make {} and [] a pain to type.
