Why does no contact increase attraction?

Me and this girl talk on and off but over time we became closer and closer. Then I stopped talking to her then Christmas rolled around and she said Merry Christmas after maybe 4 months of me being off social media. She was thrilled to hear me as I was with her. But I kept my head down and worked hard, I did things with my life and she saw that too. She started calling me "love" and using emojis with hearts and kisses. However we live so far apart from one another and have never seen one another in person.

Why does no contact increase attraction?
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