Maybe Nadal is losing his desire for tennis he's been out of the game for over six months. Nadal is so wealthy he doesn't need to play anymore for money he's won a lot of slams.
Or another theory is maybe Nadal realizes what's the point playing the Australian Open and losing early? Maybe Nadal feels he's not mentally prepared to compete again. I think Nadal is being smart he wants to be sure when he comes back he is going to be a force in the game.