We are not told explicitly why Jesus does this. Most probably it has to do with the fact that he does not want people to have the wrong idea about him. If he heals the man in the village, a lot of people will come to him for healing, preventing him from journeying to Caesarea Philippi with his disciples.
23 And he took the blind man by the hand and led him out of the village, and when he had spit on his eyes and laid his hands on him, he asked him, “Do you see anything?”