Why did the Wiggin family move from the city to rural North Carolina?

Ender's parents were devastated when he was taken from them. After two years of waiting for a letter.... for anything.... they decided to move.

No letters had ever come, and as far as they knew their own letters had never reached him. When he first was taken, Father and Mother sat at the table and keyed in long letters to him every few days. Soon, tnough, it was once a week, and when no answers came, once a month. Now it had been two years since he went,
and there were no letters, none at all, and no remembrance on his birhday. He is dead, she thought bitterly, because we have forgotten him.

But Valentine had not forgotten him. She did not let her parents know, and above all never hinted to Peter how often she thought about Ender, how often she wrote him letters that she knew he would not answer. And when Mother and Father announced to them that they were leaving the city to move to North Carolina, of all places, Valentine knew that they never expected to see Ender again. They were leaving the only place where he knew to find them.