It was all because he had wanted her to love him.
As the Doctor stood on the beach and surveyed the wreckage around him and reflected, he could think of nothing else. The knowledge choked him from the inside out as he stared at the waves. They ran up the sand and into channel dug by an unknown child then receded, beckoning him to follow.
If he could do everything over again, he would have joined her and let his fate end just as darkly, with just as much pain. That was what he deserved, after letting Rose go like that.
She hadn't deserved that.
She hadn't deserved any of it.
And he had let her die alone.