MK has a certain connection with plants, he asked Pigsy of why he bought that plant for him when he was a child, Pigsy answered with "I don't know kid. You had a look in your eyes at that time, like you were longing for something...if i didn't bought that plant, i would feel very guilty for some reason..."
With the new role of parent Wukong enjoys and learns how to take care of little MK
But he realizes that a child needs more that a mountain, peaches and the casual snacks
He needs other humans, better food and how to read and talk
Wukong decides that mk needs to be given to civilization, he chooses the one that contains his staff and leaves mk in front of a restaurant with the hope he'll find food and that someone will take him
But before leaving him he decides to wipe MK's memory of him, giving them a clean slate to grow without Wukong
Promising little Mk that one day they'll see each other again and reassuring him everything will be alright
He leaves after making sure MK is in good hands and for the next year's looks over mk while he grows and waits for the day they can be reunited again