Because, this is the one reason I can see the Doctor keeping Rose by his side, regardless of his feelings for her. Anyone else, he probably would have had leave the TARDIS way before she got to the point she did.

Reminders

She hadn't understood what he meant when he told her she reminded him of his people. She had thought it a good thing. Something that she was giving him that he wanted deeply.

Until, because of another successful attempt at using the dimension cannon and finding the right reality again, she had seen his people for herself.

Insane. Cruel. Controlling. Set in their ways.

She reminded him of his people. And he couldn't stand them. They scared him. It was the planet itself he missed.

She decided maybe that wasn't such a good thing to remind him of after all.