Because the broadcasters need politicians and courts to confirm that the TV protection money is constitutional.
It is protection money: You haven't ordered any service and if you don't pay they'll make you pay and ruin your credit score in the process.
In the collection process they pretend to be a government institution to avoid going through local courts, which sometimes are against them.
EDIT: Also, I'm beginning to wonder why any criticism of the German government or especially state TV is being downvoted here. Civil servants have a lot of time ...
It is protection money: You haven't ordered any service and if you don't pay they'll make you pay and ruin your credit score in the process.
In the collection process they pretend to be a government institution to avoid going through local courts, which sometimes are against them.
EDIT: Also, I'm beginning to wonder why any criticism of the German government or especially state TV is being downvoted here. Civil servants have a lot of time ...