Why is ignoring your EX such a powerful move at winning them back?

You would think ignoring your ex who always took you for granted when you would repsond to all her texts and always were her security blanket if the grass wasnt greener would be a bad thing to do. Why is it when you actually dont care anymore, and u really do start ignoring them, thats when they realize oh shi.t, he is serious and doesnt care. why doesnt it push them further away. why is ignoring someone such a powerful move?