Basically, Kaiser Wilhelm II uhh... Messed up pretty badly. Despite actually attempting to prevent the Great War (albeit not to a great extent), he still greatly supported the Austro-Hungarians and was basically seen as the prime instigator of the war. While it's true that his staff and the commanding officers of the army had much more influence over the war than him personally, the Kaiser was the face of Germany, and thus the one everyone held responsible. He abdicated the throne and fled to the Netherlands at the very end of the war, and never came back. The brief German Revolution spread anti Kaiser sentiment, and it was pretty obvious he was never getting Germany back. The Germans were hungry for blood, and the traitor of the Fatherland would've faced an angry mob of German citizens everywhere he went. That being said, the main reason he stayed in exile was protection. All of the allied powers that won the war demanded that the Kaiser be charged for war crimes, and the prime Minister of England even wanted him hanged. Woodrow Wilson and King George V (the Kaisers cousin), on the other hand, didn't want any harm to come to him. They just wanted him tried. Now, the Netherlands were neutral throughout the war, and so, they refused to turn him over to the allies. Thus, Kaiser Wilhelm was essentially safer there than anywhere else in the world, and that's exactly where he stayed until the day he died. It was safety. That's why he never went back to Germany. During the early years of WWII, he even sent a letter to Adolf Hitler congratulating him, but he never got a letter back. In fact, Hitler himself fought in the Great War, and expressed disgust and hatred of the man that lost the war and destroyed the German economy. Even 20 years later, he was still nearly universally hated by, not only his home country, but the entire world.

I would add that Wilhelm himself vowed not to return to Germany for as long as it remained a republic (or, rather, anything that was NOT a monarchy). The Third Reich even respected this wish of his after his death in the Netherlands in 1941 and buried him there as opposed to in Germany proper (they did display Nazi symbols at his funeral though, ignoring his other wish).

Take a look at his memoirs, he was an interesting chap, showed no remorse whatsoever for his role in the outbreak of the war, or his policies that led up to it, hated the Weimar Republic, socialists, and Jews, blamed the German people for "letting him down", genuinely expecting to be one day called back to assume the mantle of leadership once again.