Question

why is jews classified as undesirable by the nazis

Answer 1

Although Jews were the main target of Nazi hatred, they were not the only group persecuted. Other individuals and groups were considered "undesirable" and "enemies of the state.

Answer 2

because according to Hitler (Nazis) they are the finest human breeds (Aryans) on the earth but the Jews are lower than them in human physiology that's why they hate the jews so much.