You are asking the wrong question. They expect it because it's the norm in Germany. Human is psychology is such that a resume with a photo is just more memorabl

You are asking the wrong question. They expect it because it's the norm in Germany. Human is psychology is such that a resume with a photo is just more memorable, so it became the norm because applicants do it. Bias is less of a concern in a country that is historically more homogeneous.