He couldn't fix it. None of it.
Thousands of species, millions of Time Lords, billions of Daleks, trillions of possibilities for how it could have happened:
Paths into peace, and then death.
Paths into war, and then destruction.
Paths into victory, both Dalek and Time Lord … and the end of all physical reality.
Paths into standoffs, spinning back into paths of peace and war and victory yet again.
There is too much that ends, and he can fix nothing. He needs a beginning, something new and hopeful which does not need fixing, and which perhaps can fix him instead.