Why do girls stay friends with some of their ex boyfriends and not others?

It probably has to do with the ex-boyfriend, not the girl.

Maybe you’re not over her romantically, but the other guys are. I don’t know.

Not everyone is going to enjoy everyone else’s qualitys. Perhaps after she got to know you a bit better you possessed a quality that she felt its better just to stay away. No big deal. There’s a lot of girls out there that will appreciate your qualities it would be better to try and move on. She will re-assess you alls relationship one day and if she made a mistake she will try to get in contact with you again. If it was really not meant to be you’ll probably have already moved on just like she has.

Simple..she can’t get anything from you.
You are too smart for her and can see through her.
She probably realizes that?

Because you’re trying to get back with her. If I broke up with a girl and she was trying to get back with me I wouldn’t want to be friends with her I don’t think you would either. If you can walk away give her plenty of space and time, maybe you can be friends. Based on your other post, it seems like you’ve got something else in mind. which makes this question more than a little disingenuous.