Why is it Fox instead of Disney that has the rights to the third Narnia movie?

Disney dropped out because 'The Chronicles of Narnia: Prince Caspian' did not get enough money at the box-office to pay the studio back. According to the paper, "Prince Caspian" (second film) cost roughly $225 million with nearly $100 million spent on special effects. In addition, the studio spent as much as $175 million on worldwide marketing. So clearly, "Prince Caspian" did not turn out to be a winner for Disney.