The Nazis actually did try to exterminate the Jews as humane as possible. They used gas showers so the victims didn’t know what was coming and didn’t have any any visual indications of harm on their body.

Whether it was out of some perverse sense of humanity, to make the executioners sleep better or simply to improve efficiency I’m not sure.

(To be clear, I don’t condone genocide whether you try to do it humane or not)