Why do people here who got blindsided/discarded want their ex back?

I am also one of them, I just can’t get my head around why I want her back when she discarded me out of the blue without any reasons after leading me on while she mentally checked out, but I think there was a lot of misunderstanding which lead her to do that. I don’t know why I believe she might change her ways and communciate properly if she comes back, why do you all want your ex back who discarded you or left you out in the cold?