After many failed attacks and a war of attrition on the western front millions of German troops had died. This lowered the moral of the troops. After the Americans entered the war and pushed the German back and almost breaking through the Hindenburg line made it clear that the war was almost over. Also Germany had no allies left as the Austrian-Hungarian empire had dissolved and the Ottomans had lost to the British in the middle east. The Kaiser stepping down would have only lowered moral even more and would've made the German's hopeless.
