Y/n was... easy. She was easy to talk to, easy to read, easy to comfort, easy to... use. So that's exactly what everyone does. They use her. She was like a silent background character, a servant really. Klaus saw her as disposable. Elijah saw her as a vulnerability and a weakness to exploit should he have reason to go against the Mystic Falls group. And for The Rebekah? she saw her as someone to be pitied.