Information control/suppression. Some people had no idea about the scope or nature of the death and concentration camps until they were literally there; there was a deliberate propaganda effort to not raise alarm about it by pretending it was an inoffensive "relocation." "One booklet printed in 1941 glowingly reported that, in occupied Poland, German authorities had put Jews to work, built clean hospitals, set up soup kitchens for Jews, and provided them with newspapers and vocational training." (Holocaust Encyclopedia)

Later in the war, it was much harder to hide reality. But as you know, some ignorant people deny it even today.