Why do you think Graff does nothing to intervene in Ender’s behalf?

This is to prepare Ender for battle. Ender not only has to command a force but has to become this sort of man-child super soldier. All sense of innocence must be literally beaten out of him. Ender must be able to manage himself even when people on his own side want him dead. Besides, Ender is far too important to fall to some conspiracy. The powers that be would not have this.