"Why?"
The cry is desperate and harsh as the winter air, but there will be no answer. The Man in the Moon has heard the call many times over the years and he will hear it many more, but he knows he cannot reply. The path he has set Jack on is a hard one and he cannot change that. How easy it would be to comfort the child, to ask North or another to take the boy in. Jack would be happy. He would have a family again. The world would pay the price.
To make Jack happy was to give the boy attention. Attention that would draw the gaze of all upon the powerful teenager. Many would realize Jack's potential, even those who hide in shadows. The Man in the Moon knows of Pitch's secret plot. That one day the King of Fear will rise up again and that, when it happens, only an unexpected player can save them. For now, Pitch does not even know the boy exists. Even when he finds out, the dark man will think nothing of it, just another minor spirit, no threat to him.
But Jack is a threat. Jack will save them.
He can't tell the boy this. The Man in the Moon has sworn to never reveal the future to another and to give Jack any other form of happiness or comfort is to take it away from the rest of the world. It is one of the easiest choices the Guardian of Fate and Destiny will ever have to make. Doom one child to loneliness to save the rest, but it will haunt the him all the same.